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Introduction to GPS The Global Positioning System - Part 11

Other Satellite Navigation Systems GLONASS là một tất cả hệ thống dẫn đường vệ tinh thời tiết toàn cầu phát triển của Nga. Các hệ thống vệ tinh GLONASS có nhiều điểm chung với hệ thống GPS. Các chòm sao danh nghĩa của hệ thống GLONASS gồm 21 vệ tinh hoạt động cộng với ba phụ tùng danh nghĩa của một độ cao 19.100 km. Tám vệ tinh GLONASS được sắp xếp theo ba máy bay quỹ đạo (xem Hình 11.1). GLONASS quỹ đạo gần như tròn, với một khoảng thời gian quỹ đạo của 11 giờ và 15 phút và. | 11 Other Satellite Navigation Systems 11.1 GLONASS satellite system GLONASS is an all-weather global navigation satellite system developed by Russia. The GLONASS satellite system has much in common with the GPS system. The nominal constellation of the GLONASS system consists of 21 operational satellites plus three spares at a nominal altitude of 19 100 km. Eight GLONASS satellites are arranged in each of three orbital planes see Figure 11.1 . GLONASS orbits are approximately circular with an orbital period of 11 hours and 15 minutes and an inclination of 64.8 1 2 . Similar to GPS each GLONASS satellite transmits a signal that has a number of components two L-band carriers C A-code on L1 P-code on both L1 and L2 and a navigation message. However unlike GPS each GLONASS satellite transmits its own carrier frequencies in the bands 1 602-1 615.5 MHz for L1 and 1 246-1 256.5 MHz for L2 depending on the channel number. These two bands are on their way to being shifted to 1 598.0625-1 604.25 MHz and 1 242.9375-1 247.75 Mhz respectively to avoid interference with radio astronomers and operators of low-Earthorbiting satellites. With this shift each pair of GLONASS satellites will be assigned the same L1 and L2 frequencies. The satellite pairs however will 155 156 Introduction to GPS Figure 11.1 GLONASS system. Satellite image courtesy of Magellan Corporation. be placed on the opposite sides of the Earth antipodal which means that a user cannot see them simultaneously. GLONASS codes are the same for all the satellites. As such GLONASS receivers use the frequency channel rather than the code to distinguish the satellites. The chipping rates for the P-code and the C A-code are 5.11 and 0.511 Mbps respectively. The GLONASS navigation message is a 50-bps data stream which provides among other things the satellite ephemeris and the channel allocation 2 . The signal of GLONASS system is not affected by either SA or antispoofing. The GLONASS system completed 24 working satellites .