What is a satellite phone?

Satellite mobile phone is a "relay" station to establish communication in the air, and uses synchronous satellites to forward wireless signals, thus realizing global communication. Most of the general communication satellites operate in the geostationary orbit with a height of 36,000 kilometers, which is very far from the ground. The signal transmission loss between satellite and ground is large and takes a long time, which affects the authenticity and speed of the signal. Although three or four satellites in geostationary orbit can cover the whole world, they cannot cover the north and south poles of the earth. In addition, the current geostationary orbit is full of stars. More importantly, this kind of satellite phone (such as maritime satellite circuit) is as big as a suitcase and weighs 9 kilograms. And a small satellite phone like "Big Brother" is expected because it can be put in your pocket.

To this end, scientists have developed many small satellites, which are arranged in low orbit to form a satellite constellation covering the whole world. In this way, the satellite orbit is low and the required power is small, which solves the problem of miniaturization of mobile communication handsets.

In recent years, there is fierce competition among various global satellite mobile phone development plans. It is estimated that by 2002, there will be 920 communication satellites in low Earth orbit, which belong to different constellation systems. For example, the global satellite communication system, the "road in the air" global broadband system, the air Internet system, the network star system and so on. But they have only one purpose-to realize global satellite mobile communication. In other words, in the near future, cellular mobile phone base stations on land and information transmission facilities on the Internet will leave the earth and be "built" in distant space.

"The Road to the Air" is the most risky grand plan, which was put forward by Craig Mycroft, a mobile phone giant, and Bill Gates, the youngest richest man in the world.

"Road in the air" is to place 840 satellites in the sky 700,000 meters away from the earth's surface, covering every corner of the world. It makes full use of the multimedia technology of the information superhighway to integrate colorful media into a portable computer, so that it is not limited by any place, time and space when transmitting and receiving information. Through the "air road", people can participate in video teleconferences on trains, ships, cars and planes (as long as allowed); Patients can be treated by first-class medical experts in big cities in remote mountain villages, and tourists can even operate under their direct guidance. Housewives can visit world famous shops on electronic screens without leaving home, and sit on the sofa to buy their favorite clothes, furniture and other daily necessities; When students spend their holidays on pleasant beaches, they can easily surf the Internet to find the information they want, enrich their extracurricular knowledge, and receive distance education from famous universities as long as they turn on their laptops. According to experts' estimation, this huge plan is expected to be realized in 2005.

1987, the communication experts of Motorola Corporation of the United States took the lead in putting forward an amazing plan to launch a constellation consisting of 77 small satellites into space orbit 780 kilometers above the ground. These 77 small satellites are evenly distributed in seven orbits covering the whole world, and each orbit has 1 1 satellite, which can overcome the shortcomings of the current geostationary orbit communication satellites. Because there are 77 free electrons around the nucleus outside the chemical element iridium, and the mobile satellite communication system in this design consists of 77 satellites, it is very appropriate to name this system after the chemical element iridium. Later, after further accurate calculation, it was learned that 66 satellites could meet this requirement.

Some people also call iridium system reverse cellular mobile phone system. In the cellular system, the "hive" is set on the ground, and the cellular service area is fixed, while the honeycomb structure of iridium satellite system is set in space, because each satellite can project 48 beams to the surface of the earth, forming 48 cellular areas. The coverage diameter of each beam is about 600 ~ 700 kilometers, and there are 69,690 channels in each cell, so the communication capacity is extremely large and there will be no "busy" phenomenon.

Iridium system is a communication network woven by various technical means. It consists of satellite constellation, ground control management station, gateway station and user terminal. 66 satellite constellations are the core of the system, whose function is to forward radio waves; The ground control and management station and gateway station are connected with the ground public communication network, which are used to monitor and manage the attitude and working attitude of satellites, identify and verify users, provide circuit connection for communication between users, and perform switching and charging.

The satellite phone of Iridium system is similar to the mobile phone in appearance, but it has a dual working mode, including all the functions of the current cellular phone, and can also display longitude, latitude, Greenwich Mean Time and altitude. It is suitable for iridium satellite system and terrestrial cellular system. User terminals also include car phones, airborne phones, satellite pagers, fax machines and public telephone booths with iridium satellite systems.

"Iridium" system is unique in that it has advanced interstellar link connection and switching technology, which can realize signal exchange between satellites. If someone carries a satellite phone and roams between adjacent "cells", the Iridium system will transfer the signal from one satellite to another, and the data processing and exchange will be completed in space orbit. Moreover, the iridium satellite system is also seamlessly connected with the terrestrial cellular telephone network through the terrestrial gateway station, and directly utilizes the terrestrial cellular network to reasonably arrange economical and fast communication modes for users. If the user needs to make a phone call, the iridium satellite system first scans the terrestrial cellular system signal. If the user is in an uninhabited area, a remote mountainous area with backward communication or a natural disaster site, but can't receive the signal, just pull open the antenna of the mobile phone and the satellite signal will immediately fall from the sky, so that the phone can be connected and global communication can be truly realized.

1998165438+1October Iridium system was put into commercial operation. However, technological progress is not the only factor to realize the iridium project. In fact, due to the failure to adjust the business strategy in time and the unclear target users, the company cannot support huge investments and debts. Therefore, on the afternoon of March 7th, 2000 1 1: 59 EDT, the iridium satellite system stopped service.