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H Figure 29. Geographical channel overlap shown as multi- channel coverage. (This figure appeared in [40].)

Figure 29 H Figure 29. Geographical channel overlap shown as multi- channel coverage. (This figure appeared in [40].)

Related Figures (59)

§ Figure 2. Solar-powered unmanned airships. H Figure 1. The atmosphere layers.
§ Figure 2. Solar-powered unmanned airships. H Figure 1. The atmosphere layers.
M Table 1. Basic characteristics of terrestrial wireless, satellite, and HAP systems.
M Table 1. Basic characteristics of terrestrial wireless, satellite, and HAP systems.
Figure 3. Solar-powered unmanned aircraft.
Figure 3. Solar-powered unmanned aircraft.
H Figure 4. Manned aircraft.
H Figure 4. Manned aircraft.
AERIAL VEHICLES, KEY ISSUES AND SPECTRUM ALLOCATION
AERIAL VEHICLES, KEY ISSUES AND SPECTRUM ALLOCATION
M Figure 5. Unmanned fueled aircraft.
M Figure 5. Unmanned fueled aircraft.
Mi Figure 6. Wind velocity with respect to the altitude. (This figure appeared in [4].) Solar-powered unmanned aircraft and manned aircraft are also called High Altitude Aeronautical Platforms (HAAPSs).
Mi Figure 6. Wind velocity with respect to the altitude. (This figure appeared in [4].) Solar-powered unmanned aircraft and manned aircraft are also called High Altitude Aeronautical Platforms (HAAPSs).
I Figure 7. Solar power flux on a HAP at an altitude of 17 km as a function of seasonal extreme, time, and latitude. (This fig- ure appeared in [4].) HAPs are located at 17-22 km above the Earth’s surface because these altitudes are well above the air lanes, the wind conditions in the stratosphere are normally predictable (the average wind velocities are s hown in Fig. 6 with season and location variations) and, further, the zone of 17 to 22 km suffers from a relatively mild able altitudes fall from 19 to the velocities are also low. Ge turbulence. The most prefer- 22 km, while from 17 to 19 km nerally, wind velocities increase over the altitude of 25 km. Besides, as the altitude increases the air density is reduced, ma king the placement of the vehi- cle very difficult. For example, at 12 km (the maximum alti- tude of airplane lanes) the density is about 25 percent compared to that at the sea about 3.6 percent. evel, while at 24 km it is only
I Figure 7. Solar power flux on a HAP at an altitude of 17 km as a function of seasonal extreme, time, and latitude. (This fig- ure appeared in [4].) HAPs are located at 17-22 km above the Earth’s surface because these altitudes are well above the air lanes, the wind conditions in the stratosphere are normally predictable (the average wind velocities are s hown in Fig. 6 with season and location variations) and, further, the zone of 17 to 22 km suffers from a relatively mild able altitudes fall from 19 to the velocities are also low. Ge turbulence. The most prefer- 22 km, while from 17 to 19 km nerally, wind velocities increase over the altitude of 25 km. Besides, as the altitude increases the air density is reduced, ma king the placement of the vehi- cle very difficult. For example, at 12 km (the maximum alti- tude of airplane lanes) the density is about 25 percent compared to that at the sea about 3.6 percent. evel, while at 24 km it is only
i Table 3. Frequency bands allocated for LMDS or similar services (this Table appeared in [6]]).
i Table 3. Frequency bands allocated for LMDS or similar services (this Table appeared in [6]]).
' The use of this band will be reviewed in WRC-07 after further sharing studies with fixed satellite services
' The use of this band will be reviewed in WRC-07 after further sharing studies with fixed satellite services
Hi Figure 8. A general architecture of a HAP system. A general HAP architecture is illustrated in Fig. 8. ITU has proposed that footprints of a radius more than 150 km can be served from a HAP. These HAPs could cover a whole country, e.g., in [8] a structure comprising 16 HAPs was pro- posed for covering Japan with a minimum elevation angle of 10°, whereas in [9] it was mentioned that 18 HAPs can cover Greece, including all the islands. Fig. 9 presents the radius of the maximum coverage area versus the altitude of the HAP, as this was calculated in [10]. The lower the minimum eleva- tion angle, the larger the coverage area but the propagation or blocking loss becomes high at the edge of the servicing area. A practical minimum elevation angle for Broadband Wireless Access is 5°, while 15° is more commonly considered in order to avoid excessive ground clutter problems. This
Hi Figure 8. A general architecture of a HAP system. A general HAP architecture is illustrated in Fig. 8. ITU has proposed that footprints of a radius more than 150 km can be served from a HAP. These HAPs could cover a whole country, e.g., in [8] a structure comprising 16 HAPs was pro- posed for covering Japan with a minimum elevation angle of 10°, whereas in [9] it was mentioned that 18 HAPs can cover Greece, including all the islands. Fig. 9 presents the radius of the maximum coverage area versus the altitude of the HAP, as this was calculated in [10]. The lower the minimum eleva- tion angle, the larger the coverage area but the propagation or blocking loss becomes high at the edge of the servicing area. A practical minimum elevation angle for Broadband Wireless Access is 5°, while 15° is more commonly considered in order to avoid excessive ground clutter problems. This
a Figure 9. Radius of the maximum coverage area as a function of the HAP’s altitude.
a Figure 9. Radius of the maximum coverage area as a function of the HAP’s altitude.
§ Figure 11. The architecture scenario of the HeliNet network.
§ Figure 11. The architecture scenario of the HeliNet network.
BH Figure 10. A cellular architecture.
BH Figure 10. A cellular architecture.
§ Figure 12. Cell forming according to traffic.
§ Figure 12. Cell forming according to traffic.
l Figure 14. Example of theoretical sectorization pattern with two outer circles. m Figure 13. The aerial cell.
l Figure 14. Example of theoretical sectorization pattern with two outer circles. m Figure 13. The aerial cell.
B Table 7. Number of cells served by an individual backhaul link for the 28GHz band, using a 2° steer- able ground antenna at 30km ground distance (this Table appeared in [14]).
B Table 7. Number of cells served by an individual backhaul link for the 28GHz band, using a 2° steer- able ground antenna at 30km ground distance (this Table appeared in [14]).
§ Figure 16. Cell scanning.
§ Figure 16. Cell scanning.
a Figure 15. Ring-shaped cells.
a Figure 15. Ring-shaped cells.
H Figure 17. A HAPs-based system for maritime services.
H Figure 17. A HAPs-based system for maritime services.
H Figure 19. Minimum bandwidth required for a 10 Mb/s user for a given C/N, (Shannon Equation Rp/W = log) (1+ C/No).) (This is figure appeared in [6].)
H Figure 19. Minimum bandwidth required for a 10 Mb/s user for a given C/N, (Shannon Equation Rp/W = log) (1+ C/No).) (This is figure appeared in [6].)
B Figure 20. Interference in a ground terminal in the case of a multiple HAPs scenario. The improvement in spectrum utilization for broadband services in mm-wave bands using multiple high-altitude plat- forms was investigated in [23]. HAPs can never be as spec- trally efficient as terrestrial broadband systems because the minimum size of their cell is limited by the maximum size of the antenna that can be accommodated on the platform. However, the user antenna can be highly directive, allowing a good spatial discrimination between HAPs in a HAP con- stellation. The increase of capacity for multiple platform configurations was studied in [23], and results for the sce- nario of one beam (cell) per HAP were given. In Fig. 20 the main HAP and one interfering HAP are shown. The perfor- mance of the single cell, multiple HAP scenario was assessed for different numbers of HAPs, different HAPs spacing radii, and user antennas with a range of directionalities. The CIR (carrier to interference ratio) was determined across the coverage area and then converted into bandwidth effi- ciency (n ~ log (1 + CIJR)). As the number of HAPs increas- es, CIR becomes worse. In addition, an increase in the HAPs spacing radius does not impact on CIR. As for the
B Figure 20. Interference in a ground terminal in the case of a multiple HAPs scenario. The improvement in spectrum utilization for broadband services in mm-wave bands using multiple high-altitude plat- forms was investigated in [23]. HAPs can never be as spec- trally efficient as terrestrial broadband systems because the minimum size of their cell is limited by the maximum size of the antenna that can be accommodated on the platform. However, the user antenna can be highly directive, allowing a good spatial discrimination between HAPs in a HAP con- stellation. The increase of capacity for multiple platform configurations was studied in [23], and results for the sce- nario of one beam (cell) per HAP were given. In Fig. 20 the main HAP and one interfering HAP are shown. The perfor- mance of the single cell, multiple HAP scenario was assessed for different numbers of HAPs, different HAPs spacing radii, and user antennas with a range of directionalities. The CIR (carrier to interference ratio) was determined across the coverage area and then converted into bandwidth effi- ciency (n ~ log (1 + CIJR)). As the number of HAPs increas- es, CIR becomes worse. In addition, an increase in the HAPs spacing radius does not impact on CIR. As for the
H Table 9. Basic wireless terrestrial and HAP channel parameters. Regarding channel modeling in HAP systems, a physical! statistical model for macro- and megacellular propagation was developed in [25, 26] for IMT-2000 communications systems in the S-Band (1550-5200 MHz) and validated by experimen- tal measurements at 1.6 GHz. Particularly, in [25] a method was developed to predict the coverage area, considering the fade depth as a function of the coverage diameter for differ-
H Table 9. Basic wireless terrestrial and HAP channel parameters. Regarding channel modeling in HAP systems, a physical! statistical model for macro- and megacellular propagation was developed in [25, 26] for IMT-2000 communications systems in the S-Band (1550-5200 MHz) and validated by experimen- tal measurements at 1.6 GHz. Particularly, in [25] a method was developed to predict the coverage area, considering the fade depth as a function of the coverage diameter for differ-
a Figure 22. Attenuation due to dry air and H,0 as a function of the frequency. i Figure 21. Attenuation due to rain, mist, water vapor, and oxygen as a function of the frequency.
a Figure 22. Attenuation due to dry air and H,0 as a function of the frequency. i Figure 21. Attenuation due to rain, mist, water vapor, and oxygen as a function of the frequency.
I Table 10. Rainfall rates for different climate zones which are exceeded for 0.01 percent of the time.
I Table 10. Rainfall rates for different climate zones which are exceeded for 0.01 percent of the time.
a Figure 23. The effect of rain on signal attenuation at 30 GHz for ground distances 0-50 km. Vertical lines indicate rain rates for typical climate zones that must be tolerated to achieve an availability of 99.99%. (This figure appeared in [6].)
a Figure 23. The effect of rain on signal attenuation at 30 GHz for ground distances 0-50 km. Vertical lines indicate rain rates for typical climate zones that must be tolerated to achieve an availability of 99.99%. (This figure appeared in [6].)
i Figure 24. Geometry of rain scattering. The radiation beamed toward user B is scattered by the rain and causes co-channel interference to user A, who is located in another cell.
i Figure 24. Geometry of rain scattering. The radiation beamed toward user B is scattered by the rain and causes co-channel interference to user A, who is located in another cell.
lM Figure 25. HAPs uplink interference geometry.
lM Figure 25. HAPs uplink interference geometry.
i Figure 27. Effect of sidelobe level on coverage for one of four and seven channels. (This figure appeared in [40].) i Figure 26. |sinc3Bx| antenna performance. Total ground cov- erage for a 10-degree boresight separation angle of co-channel antennas. Coverage is dependent on the required ground CIR. The white areas indicate CIR below 0 dB. (This figure appeared in [39].)
i Figure 27. Effect of sidelobe level on coverage for one of four and seven channels. (This figure appeared in [40].) i Figure 26. |sinc3Bx| antenna performance. Total ground cov- erage for a 10-degree boresight separation angle of co-channel antennas. Coverage is dependent on the required ground CIR. The white areas indicate CIR below 0 dB. (This figure appeared in [39].)
i Figure 28. CIR profile through center of service area for side- lobes at —40 dB. (This figure appeared in [36].)
i Figure 28. CIR profile through center of service area for side- lobes at —40 dB. (This figure appeared in [36].)
Hi Figure 30. Interference from HAPs to a GEO satellite. is reduced for the majority of the coverage area. This means that for a certain CIR threshold, the scheme with seven chan- nels achieves a greater coverage area. In other words, when for the four-channel scheme there is not multichannel cover- age at the cell edges, the seven-channel scheme presents multibeam coverage, which can be useful for a handoff mechanism. Figure 27 illustrates the fractional simultaneous coverage for the cases of -40 and —50 dB sidelobe levels, Fig. 28 presents the CIR profile through the center of the cover- age area for sidelobe at —40 dB, while in Fig. 29 the geograph-
Hi Figure 30. Interference from HAPs to a GEO satellite. is reduced for the majority of the coverage area. This means that for a certain CIR threshold, the scheme with seven chan- nels achieves a greater coverage area. In other words, when for the four-channel scheme there is not multichannel cover- age at the cell edges, the seven-channel scheme presents multibeam coverage, which can be useful for a handoff mechanism. Figure 27 illustrates the fractional simultaneous coverage for the cases of -40 and —50 dB sidelobe levels, Fig. 28 presents the CIR profile through the center of the cover- age area for sidelobe at —40 dB, while in Fig. 29 the geograph-
i Figure 31. Improvement of the radiation pattern of an on- board antenna by beam shaping.
i Figure 31. Improvement of the radiation pattern of an on- board antenna by beam shaping.
Bf Figure 33. Minimum number of users with UMTS CDMA. (These figures appeared in [10].) Transmission/coding techniques have always constituted an issue of paramount importance in every communication system. The HeliNet project aimed at the evaluation of linear and non-linear modulation schemes (QPSK, QAM, M-APSK (starQAM), CPM, GMSK, and MA-MSK). The modulation schemes were evaluated in the non-linear region of the transmitted power amplifier. Suitable Forward Error Correction (FEC) coding Regarding interference from/to other systems, we can dis- tinguish the following cases of interference paths: between HAPs ground stations and other terrestrial stations or satellite earth stations; between HAPs ground stations and space sta- tions, i.e. satellites; between HAPs on-board stations and other terrestrial stations; and finally between HAPs on-board stations and space stations. Studies [9, 41] dealt with the inter- ference from a HAPs-based network to a GEO network (Fig. 30) and the interference from a GEO Earth station to a HAP gateway. The authors in [41] investigated the interference at 31/28 GHz in Japan, while in [9] the interference at 47 GHz was examined for a potential use of HAPs in Greece. Both studies showed that the interference level was acceptable in both scenarios. Moreover, in [42, 41] interference mitigation techniques were presented. It was shown that the interference to GEO services can be reduced by improving the radiation pattern of the on-board antenna by beam shaping (Fig. 31). While for the case of HAPs ground stations interfering with other ground services, the minimum elevation angle could be increased (Fig. 32). A mitigation technique was described in 42] that is a modified Maximal-Ratio-Combining (MRC) beamformer for on-board digital beamforming (DBF). It was
Bf Figure 33. Minimum number of users with UMTS CDMA. (These figures appeared in [10].) Transmission/coding techniques have always constituted an issue of paramount importance in every communication system. The HeliNet project aimed at the evaluation of linear and non-linear modulation schemes (QPSK, QAM, M-APSK (starQAM), CPM, GMSK, and MA-MSK). The modulation schemes were evaluated in the non-linear region of the transmitted power amplifier. Suitable Forward Error Correction (FEC) coding Regarding interference from/to other systems, we can dis- tinguish the following cases of interference paths: between HAPs ground stations and other terrestrial stations or satellite earth stations; between HAPs ground stations and space sta- tions, i.e. satellites; between HAPs on-board stations and other terrestrial stations; and finally between HAPs on-board stations and space stations. Studies [9, 41] dealt with the inter- ference from a HAPs-based network to a GEO network (Fig. 30) and the interference from a GEO Earth station to a HAP gateway. The authors in [41] investigated the interference at 31/28 GHz in Japan, while in [9] the interference at 47 GHz was examined for a potential use of HAPs in Greece. Both studies showed that the interference level was acceptable in both scenarios. Moreover, in [42, 41] interference mitigation techniques were presented. It was shown that the interference to GEO services can be reduced by improving the radiation pattern of the on-board antenna by beam shaping (Fig. 31). While for the case of HAPs ground stations interfering with other ground services, the minimum elevation angle could be increased (Fig. 32). A mitigation technique was described in 42] that is a modified Maximal-Ratio-Combining (MRC) beamformer for on-board digital beamforming (DBF). It was
Figure 32. Increase of the minimum operational elevation angle.
Figure 32. Increase of the minimum operational elevation angle.
B Figure 34. Typical examples of multibeam footprints proposed in the ITU-R recommendation: a) elliptical-beam uniform footprint model (367 beams); b) circular-beam multizone footprint model (397 beams). § Table 11. Four transmission options and their suitability for broadband services (this Table appeared in [7]]).
B Figure 34. Typical examples of multibeam footprints proposed in the ITU-R recommendation: a) elliptical-beam uniform footprint model (367 beams); b) circular-beam multizone footprint model (397 beams). § Table 11. Four transmission options and their suitability for broadband services (this Table appeared in [7]]).
Hl Figure 36. Basic configuration of prototype multibeam antennas (in case of receiving): a) multi- beam horn (MBH) antenna; b) digital beamforming (DBF) antenna. (This figure appeared in [3].) Considering the movement of HAPs we see that it is nec- essary to compensate this movement by mechanical or elec- tronic steering. A serious constraint is the available payload aperture. As the size of cells decreases, their number increas- es and also the required payload aperture increases. The structure size of an antenna array was calculated in [10] as a function of the radius of the central cell (broadside cell), for a Two types of multibeam antennas meeting the above requirements were described in [3, 8, 46]: a Multibeam Horn (MBH) antenna of the mechanical-drive type for operation at 48/47 GHz, and a Digital Beamforming (DBF) antenna of the electronic-scanning type for operation at 31/28 GHz. Basic configurations of the antennas are shown in Fig. 36, and the basic specifications of the respective antennas are presented
Hl Figure 36. Basic configuration of prototype multibeam antennas (in case of receiving): a) multi- beam horn (MBH) antenna; b) digital beamforming (DBF) antenna. (This figure appeared in [3].) Considering the movement of HAPs we see that it is nec- essary to compensate this movement by mechanical or elec- tronic steering. A serious constraint is the available payload aperture. As the size of cells decreases, their number increas- es and also the required payload aperture increases. The structure size of an antenna array was calculated in [10] as a function of the radius of the central cell (broadside cell), for a Two types of multibeam antennas meeting the above requirements were described in [3, 8, 46]: a Multibeam Horn (MBH) antenna of the mechanical-drive type for operation at 48/47 GHz, and a Digital Beamforming (DBF) antenna of the electronic-scanning type for operation at 31/28 GHz. Basic configurations of the antennas are shown in Fig. 36, and the basic specifications of the respective antennas are presented
| Figure 35. The size of a square array antenna as a function o the radius of the central cell for a HAP operating at 2.2 GHz and at an altitude of 21 km. (This figure appeared in [10].)
| Figure 35. The size of a square array antenna as a function o the radius of the central cell for a HAP operating at 2.2 GHz and at an altitude of 21 km. (This figure appeared in [10].)
M@ Table 12. Main specifications of the multibeam antenna prototypes (this table appeared in [3])
M@ Table 12. Main specifications of the multibeam antenna prototypes (this table appeared in [3])
i Figure 37. Prototypes of multibeam antennas: a) MBH antenna (R,) (seven elements, 47/48 GHz band); b) DBF antenna (R,) (16 elements, 28/31 GHz band). (This photo appeared in [8].) action becomes necessary. With this antenna, each element requires an aperture, as each element acts as a directional antenna. When the antenna is composed of a few dozen or hundreds of elements, the antenna becomes oversized, and the number of cables connecting the repeater and the respec- tive antenna also increases, making the gimbal difficult to rotate because the Radio Frequency (RF) cables may be twisted. Therefore, this antenna is considered not to be partic- ularly suitable for a large-scale multibeam antenna applica- tion. To overcome the twisted cable problems, an improved mechanical control mechanism was developed. It employed individual steering mechanism for each of the horn antennas instead of the gimbal control mechanism in order to keep the footprint of the beams fixed even with the platform rotation in the horizontal plane. The steering motions of the antennas were linked to each other, so that only one motor could drive all the antennas in the horizontal plane in principle. General- ly, this antenna lacks flexibility, relative to the DBF antenna discussed below. perience" a _ The main features of the MBH antenna [3 8, 46] are the broad bandwidth (depending on existing technology), the excellent wide-angle characteristics of gain and axial ratio, and the comparatively low development expense. The footprints of this antenna are fixed cells, so using a different frequency for each beam results in four or seven frequencies in the spatia domain. Furthermore, the antenna must feature a sufficiently low side-lobe level. Considering the movement of a ground user terminal or the drift of the HAP (due to variations in atmospheric pressure or wind), it is obvious that a handoff
i Figure 37. Prototypes of multibeam antennas: a) MBH antenna (R,) (seven elements, 47/48 GHz band); b) DBF antenna (R,) (16 elements, 28/31 GHz band). (This photo appeared in [8].) action becomes necessary. With this antenna, each element requires an aperture, as each element acts as a directional antenna. When the antenna is composed of a few dozen or hundreds of elements, the antenna becomes oversized, and the number of cables connecting the repeater and the respec- tive antenna also increases, making the gimbal difficult to rotate because the Radio Frequency (RF) cables may be twisted. Therefore, this antenna is considered not to be partic- ularly suitable for a large-scale multibeam antenna applica- tion. To overcome the twisted cable problems, an improved mechanical control mechanism was developed. It employed individual steering mechanism for each of the horn antennas instead of the gimbal control mechanism in order to keep the footprint of the beams fixed even with the platform rotation in the horizontal plane. The steering motions of the antennas were linked to each other, so that only one motor could drive all the antennas in the horizontal plane in principle. General- ly, this antenna lacks flexibility, relative to the DBF antenna discussed below. perience" a _ The main features of the MBH antenna [3 8, 46] are the broad bandwidth (depending on existing technology), the excellent wide-angle characteristics of gain and axial ratio, and the comparatively low development expense. The footprints of this antenna are fixed cells, so using a different frequency for each beam results in four or seven frequencies in the spatia domain. Furthermore, the antenna must feature a sufficiently low side-lobe level. Considering the movement of a ground user terminal or the drift of the HAP (due to variations in atmospheric pressure or wind), it is obvious that a handoff
lM Figure 38. CIR contours for one channel of four: a) circular beams; b) optimized elliptic beams. (This figure appeared in [40].)
lM Figure 38. CIR contours for one channel of four: a) circular beams; b) optimized elliptic beams. (This figure appeared in [40].)
I Figure 39. Power margin required to overcome the effects of worst case platform displacement with steerable fixed station antennas for different ground distances and a rainfall rate of 28 mm/h. (This figure appeared in [6].)
I Figure 39. Power margin required to overcome the effects of worst case platform displacement with steerable fixed station antennas for different ground distances and a rainfall rate of 28 mm/h. (This figure appeared in [6].)
B Figure 40. Power margin required to overcome the effects of worst case platform displacement with fixed FS antennas (5° beamwidth) for different ground distances and a rainfall rate of 28 mm/h. (This figure appeared in [6].)
B Figure 40. Power margin required to overcome the effects of worst case platform displacement with fixed FS antennas (5° beamwidth) for different ground distances and a rainfall rate of 28 mm/h. (This figure appeared in [6].)
| Figure 41. A modulated retro-directive passive transponder placed on a HAP and illumi- nated by a ground station. (This figure appeared in [52].)
| Figure 41. A modulated retro-directive passive transponder placed on a HAP and illumi- nated by a ground station. (This figure appeared in [52].)
satellite formats could be used. The choice of network proto- cols (such as TCP/IP, Wireless ATM, Wireless IP, and HIPERACCESS protocols) should be made on the basis of network topology (integration with terrestrial and satellite networks). Considering the movement of user terminals, or even the movement of the HAP, suitable handoff algorithms should be specified for different cell sizes and steerability of the on-board antenna array.
satellite formats could be used. The choice of network proto- cols (such as TCP/IP, Wireless ATM, Wireless IP, and HIPERACCESS protocols) should be made on the basis of network topology (integration with terrestrial and satellite networks). Considering the movement of user terminals, or even the movement of the HAP, suitable handoff algorithms should be specified for different cell sizes and steerability of the on-board antenna array.
H Figure 43. The HeliNet network architecture. In [46] a new channel access technology for HAP commu- nication networks, called Space Division Multiple Access (SDMA), was discussed. SDMA is a combination of TDMA, FDMA, and CDMA schemes with on-board multibeam anten- nas. According to that technique, the same channel, the same time slot, and the same code can be shared by different user terminals located at different areas, enhancing in that way the frequency reuse strategies. Uplink and downlink frames have the same duration, but uplink and downlink channels may have different bandwidths. There are two kinds of time slots, one for control information and one for transmitting data, with the length of the data slot being larger. Multimedia traf- fic can be supported due to the demand-based data slots assignment.
H Figure 43. The HeliNet network architecture. In [46] a new channel access technology for HAP commu- nication networks, called Space Division Multiple Access (SDMA), was discussed. SDMA is a combination of TDMA, FDMA, and CDMA schemes with on-board multibeam anten- nas. According to that technique, the same channel, the same time slot, and the same code can be shared by different user terminals located at different areas, enhancing in that way the frequency reuse strategies. Uplink and downlink frames have the same duration, but uplink and downlink channels may have different bandwidths. There are two kinds of time slots, one for control information and one for transmitting data, with the length of the data slot being larger. Multimedia traf- fic can be supported due to the demand-based data slots assignment.
I Figure 44. Average throughput over a 230 sec transmission in the case of a mixed infrastructure comprising HAPs/UAVs and a GEO satellite. (This figure appeared in [58].)
I Figure 44. Average throughput over a 230 sec transmission in the case of a mixed infrastructure comprising HAPs/UAVs and a GEO satellite. (This figure appeared in [58].)
H Figure 45. Received power dynamics. (This figure appeared in [48].)
H Figure 45. Received power dynamics. (This figure appeared in [48].)
lM Figure 46. A terrestrial cellular network integrated with a cell by an aerial platform (macrocell). (This figure appeared in [59].)
lM Figure 46. A terrestrial cellular network integrated with a cell by an aerial platform (macrocell). (This figure appeared in [59].)
i Figure 47. System architecture for provision of integrated services. (This fig- ure appeared in [59].) Recently some projects focusing on aerial vehicles in the stratosphere have been funded. HeliNet was a project based upon high altitude very long endurance unmanned solar aero- dynamic platforms, funded by the European Commission’s 5th program. In the framework of the HeliNet project [62], a small prototype solar powered airframe was partially devel- oped in conjunction with some key elements of power and propulsion systems. The prototype was based on the design of an unmanned solar-powered aircraft, named Heliplat. Heliplat was especially tailored for long endurance operations at an altitude of 17 km, supporting a payload of 100 kg and offering total available power for telecommunications applications of
i Figure 47. System architecture for provision of integrated services. (This fig- ure appeared in [59].) Recently some projects focusing on aerial vehicles in the stratosphere have been funded. HeliNet was a project based upon high altitude very long endurance unmanned solar aero- dynamic platforms, funded by the European Commission’s 5th program. In the framework of the HeliNet project [62], a small prototype solar powered airframe was partially devel- oped in conjunction with some key elements of power and propulsion systems. The prototype was based on the design of an unmanned solar-powered aircraft, named Heliplat. Heliplat was especially tailored for long endurance operations at an altitude of 17 km, supporting a payload of 100 kg and offering total available power for telecommunications applications of
H Figure 48. HAPs for military applications.
H Figure 48. HAPs for military applications.
M Figure 49. The HALO network. (This figure appeared in [18].)
M Figure 49. The HALO network. (This figure appeared in [18].)
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