CC BY
11УДК 52(15)
P. Dankov Sofia University, Bulgaria, Sofia
M. Gachev RaySat Bulgaria Ltd., Bulgaria, Sofia
O. Ognyanov
Cluster for AeroSpace Technology, Research and Applications, Bulgaria, Sofia
IMPROVEMENT OF THE COMMUNICATION FUNCTION OF SMALL UNIVERSITY SATELLITES FOR SUPPORT OF HUMAN ACTIVITIES IN THE POLAR REGIONS
The necessity for development of the so-called communication function of university small satellites is considered in this paper. This function can be successfully applied to serve the increasing needs of backhaul and off-line operational communications in the both polar regions. Suitable frequency bands, on-board and ground-station antennas and achievable data throughput are discussed.
Communications with the polar regions have been always a big challenge. The up-to-date solutions are more or less limited: the short-wave amateur radio is extremely slow and influenced by weather conditions; the commercial mobile-phone satellite systems are expensive and suitable for voice calls only (data can be sent at unacceptable low bit rate 2.4 kbps); finally, communications through GEO «inclined» satellites (1-1.5 Mbps) (the best solution at the moment) are time and space restricted and unstable (satellites permanently change the position and expensive tracking systems are needed). That is why, the use of non-GEO systems is a promising alternative. We propose in this paper an improvement of the communication function [1] of the small university satellites at close-to-circular orbit for maintenance of stable backhaul communications for the inhabitants, scientific expeditions' members, ship's companies, etc. in the both polar regions. The needs of communications at higher bit rates will increase in these regions in the next years due to different reasons. The faster ice melting in the Arctic already «opens» new transportation routes (North-West, North-East and North-North passages [2]). As a result, increased navigation and activities related to fishing, oil and gas industries are already observed. At the opposite globe side, a wide continent Antarctica (across 4 000 km) exists, populated with many scientific stations (~4 000 people in summer and ~1 000 in winter) located mainly on the coast line [3], and ships navigating in the polar seas. The different users' profile in the both regions specifies the needs for different types of communications. The needs of operational communications (voice call for safety and logistics, online Supervisory Control and Data Acquisition, Internet access) will be decisive for the new transportation corridors in Arctic and for the navigation near the Antarctic coast. Contrariwise, the need of fast backhaul communications (less time-critical scientific and other data transfer based on «store-and-forward» technology) will be considerably greater for the Antarctic expeditions in the next few years.
The university small satellites with well-developed two-way communication function can fill this «gap» of needs for backhaul and off-line operational communication with the Arctic and Antarctic regions.
First of all, the operational frequency for the downlink (space-Earth) (DL) channels should considerable increase (C, X, Ka band), because the lower-frequency bands (UHF, L and even S), suitable for telemetry applications, are extremely congested [4] and the bit rate is limited (max. to 55 kbps in UHF band and 5 Mbps in S-band). International Telecommunication Union (ITU) has allocated a lot of frequency bands for amateur-satellite services ASS [5] above L band (most of them accepted by the national spectrum management organizations, [6]): 2.40...2.45, 5.65...5.67 (E-s), 5.83...5.85 (s-E), 10.45... 10.5; 24.24.05 GHz, etc. Part of these bands coincides with the free ISM bands. We have to add also the frequency bands, assigned for EESS (Earth exploration) and similar applications: 8.025.8.40 (s-E), 25.5.27 (s-E), 28.5.29.1 (E-s), 29.5.29.9 GHz (Es), etc. Table 1 presents data for the achievable bit rate in the effective bandwidth BW due to Doppler shift using
BPSK or QPSK modulations (without additional codding-gain or spread-spectrum schemes). 7.14-Mbps bit rate is possible in 10-MHz BW, but bit rates above 70 or even 100 Mbps are achievable at BW >50 MHz in Ka band (using data coding [7]). The other important condition for achieving of high bit rate is the utilization of higher-gain on-board patch antenna array and steerable ground station antenna panel [8] - see data in Table 2. We propose the use of 2 or 4 patch planar antenna arrays in the X band (instead of single patch, see the literature survey in [9]) for the on-board Tx/Rx systems, arranged in 5 pairs on 5-face switchable antenna panels on mechanical support with truncated pyramidal shape (Fig. 5, 6 in [1]). Thus, if we apply the concept for the time extended data transfer communication sessions between the small satellite and the ground station [1]: three sessions at the so-called base orbit exactly over the ground station for 8.10 min. (at 600 km orbit altitude) and two additional sessions at side orbits (at 1 000.1 500 km aside the given ground station), the total daily throughput can reach the value of 30.50 GB. At 1 500-km orbit altitude the data throughput is 5-6 times smaller (at typically 11-Mbps bit rate), but enough for the backhaul communication purposes for one ground station in the polar regions.
Решетневскце чтения
Table 1
Maximal achievable bit rate for BPSK/QPSK modulations in the effective bandwidth BW due to Doppler shift
Frequency band, GHz Max permited BW, MHz [б] Max Doppler shift, kHz* Min.effective BWeff, MHz* Max bit rate rb, Mbps Needed gross bit rate Rb, dB.bps
BPSK* QPSK* BPSK QPSK
2.427...2.443 1Q ±5б.1/4б.8 9.89/9.95 7.4/7.5 14.8/14.9 б8.7 71.7
5.762.5.785 Q.15 ±133.1/111.Q - - - - -
10.370...10.450 1Q ±239.9/2QQ.Q 9.52/9.6Q 7.1/7.2 14.3/14.4 б8.5 71.5
24.Q5Q_24.25Q 1Q ±55б.б/4б3.9 8.89/9.Q7 б.7/б.8 13.3/13.б б8.2 71.2
8.025...8.175 5Q** ±18б.7/155.б 49.б2/49.б9 37.2/37.3 74.4/74.5 75.7 78.7
25.5...27.0 5Q** ±6Q5.Q/5Q4.3 48.79/48.99 3б.5/3б.7 73.Q/73.5 75.б 78.б
* Pair of parameters for 600/1 500 km orbit altitudes. ** Available channel bandwidth for EESS frequency bands.
Table 2
Available Eb / N0 and margin M, dB, in the downlink channel DL for QPSK modulation, using planar patch on-board antennas with fixed gain 10 dB and equivalent dish antennas with diameter 1.2 m for the ground station
f, GHz/ BW, MHz Altitude, km Path losses, dB C/N0, dB.Hz (Available Eb/ N0; Margin M, dB) for DL channel [Psat = 1 W] Required Pm, (for [Ei/Nq = = 9.6 dB; M = 3.5 dB]
2.435/1Q 6QQ/15QQ 155.7/163.7 94.8Q/86.84 (23.10; 13.50) / (15.11; 5.51) Psat = 0.100 / 0.630
1Q.41/1Q 6QQ/15QQ 168.4/176.3 94.8Q/86.84 (23.24; 13.64) / (15.25; 5.65) Psat = 0.097/ 0.609
24.15/1Q 6QQ/15QQ 175.7/183.6 94.8Q/86.84 (23.56; 13.96) / (15.50; 5.90) Psat = 0.090 / 0.575
26.25/5Q 6QQ/15QQ 176.4/184.3 94.8Q/86.84 (16.17; 6.57) / (8.18; -1.42) Psat = 0.494 / 3.11
Special thanks to the National Research Fund of Bulgaria, to the Rector of Sofia University Prof. I. Ilchev and to the Rector of SibSAU, Krasnoyarsk Prof. I. Kovalev for their valuable support.
References
1. Small Communication Satellite Mission for Enhancement of Antarctic Investigations / P. Dankov [et. al.] // UN/Japan Nanosatellite Symp. Nagoya, Japan, 2012.
2. Cheffena M, High-Capacity Radio Communication for the Polar Region: Challenges and Potential Solutions // IEEE Antennas and Propagation Mag. 2012. Vol. 54, № 2. Р. 238-244.
3. The Business Case for Delivering Broadband to the Antarctic Using Micro-Satellites / D. Faber, M. Brett, J. Kingt et. al. // Proc. the Intern. Astronautical Cong. Cape Town, South Africa, 2011.
4. The Radio Amateur Satellite Corporation [Electronic resource]. URL: http://www.amsat.org/amsat-new/satellites/frequencies.php (date of visit: 20.08.2012).
5. ITU-R, Amateur and Amateur-Satellite Services [Electronic resource]. URL: http://www.itu.int/en/ITU-R/space/AmateurDoc/AmateurSatServictFreq.pdf (date of visit: 20.08.2012).
6. Решение № 10-07-01 (2010) гос. комиссии по радиочастотам Минкомсвязи Рос. Федерации [Электронный ресурс]. URL: http://minsvyaz.ru/ru/doc/?id_4=477 (дата обращения: 20.08.2012).
7. Nanosat Ka-Band Communications - A Paradigm Shift in Small Satellite Data Throughput / A. King, J. Ness, G. Bonin et. al. // 26th Annual AIAA/USU Conf. on Small SatelW^ Logan, Utah, 2012.
8. Ray Sat antenna systems, Satcom on-the-move [Electronic resource]. URL: http://www.raysat.com/ (date of visit: 20.08.2012).
9. Kakoyiannis C., Constantinou P. Electrically Small Microstrip Antennas Targeting Miniaturized Satellites: Cube-Sat Paradigm // Microstrip Antennas. 2011. P. 273-316.
П. Данков
Софийский университет, факультет физики, Болгария, София
М. Гачев
RaySat Bulgaria Ltd., Болгария, София
О. Огнянов
CASTRA (Cluster for AeroSpace Technology, Research and Applications), Болгария, София
СОВЕРШЕНСТВОВАНИЕ ФУНКЦИЙ СВЯЗИ МАЛЫХ СТУДЕНЧЕСКИХ СПУТНИКОВ ДЛЯ УЧАСТИЯ В РАБОТЕ ЗА ПОЛЯРНЫМ КРУГОМ
Рассматривается важность разработки коммуникационных функций малых студенческих спутников. Данная функция может успешно применяться для решения задач связи в районах Арктики и Антарктики. Обсуждаются диапазоны частот, функционирование наземных антенн и антенн, размещенных на малых космических аппаратах, скорость обработки полученной информации.
© Dankov P., Gachev M., Ognyanov O., 2012
