Low Altitude Satellite Constellation for Futuristic Aerial-Ground Communications

This paper discusses the significance and prospects of low altitude small satellite aerial vehicles to ensure smooth aerial-ground communications for next-generation broadband networks.To achieve the generic goals of fifthgeneration and beyondwireless networks,the existing aerial network architecture needs to be revisited.The detailed architecture of low altitude aerial networks and the challenges in resource management have been illustrated in this paper.Moreover,we have studied the coordination between promising communication technologies and low altitude aerial networks to provide robust network coverage.We talk about the techniques that can ensure userfriendly control and monitoring of the low altitude aerial networks to bring forth wireless broadband connectivity to a new dimension.In the end,we highlight the future research directions of aerial-ground communications in terms of access technologies,machine learning,compressed sensing,and quantum communications.

Beam Position and Beam Hopping Design for LEO Satellite Communications

The numbers of beam positions(BPs)and time slots for beam hopping(BH)dominate the latency of LEO satellite communications.Aiming at minimizing the number of BPs subject to a predefined requirement on the radius of BP,a low-complexity user density-based BP design scheme is proposed,where the original problem is decomposed into two subproblems,with the first one to find the sparsest user and the second one to determine the corresponding best BP.In particular,for the second subproblem,a user selection and smallest BP radius algorithm is proposed,where the nearby users are sequentially selected until the constraint of the given BP radius is no longer satisfied.These two subproblems are iteratively solved until all the users are selected.To further reduce the BP radius,a duplicated user removal algorithm is proposed to decrease the number of the users covered by two or more BPs.Aiming at minimizing the number of time slots subject to the no co-channel interference(CCI)constraint and the traffic demand constraint,a low-complexity CCI-free BH design scheme is proposed,where the BPs having difficulty in satisfying the constraints are considered to be illuminated in priory.Simulation results verify the effectiveness of the proposed schemes.

Primary Analysis of Development Approach to Chinese Satellite Mobile Communication

The paper describes the development of mobile communication first and then points out that it is necessary for China to develop satellite mobile communication after comparing the cellular mobile communication with the satellite mobile communication. After comparing the geostationary satellite system with the low earth orbit satellite mobile communication system, as well as the single-beam system with the multibeams system, both used in satellite mobile communication, we suggest that China, according to its economic status and level of satellite technology, should develop a geostationary multibeam satellite for its domestic mobile communication.

基于ORBCOMM卫星机会信号的定位技术

为摆脱对全球导航卫星系统(GNSS)的依赖,克服其有意或无意干扰情况下无法工作等问题,可采用机会信号(SOP)实现定位,低轨卫星机会信号具备信号功率高、覆盖性广及无需增建基础设施等优点。提出了利用轨道通信卫星(ORBCOMM)系统实现天基机会信号定位。通过对ORBCOMM卫星机会信号的通信体制进行深入研究,实现了利用ORBCOMM卫星机会信号获取多普勒测量信息,建立了瞬时多普勒定位及其几何精度因子的数学模型,并采用卫星TLE数据结合轨道预测模型获得的卫星轨道信息实现ORBCOMM卫星机会信号定位。实测结果表明:利用ORBCOMM卫星机会信号可实现精度优于140 m的定位。研究成果对基于天基机会信号定位技术的理论研究及应用具有重要意义。

DOA estimation for attitude determination on communication satellites

In order to determine an appropriate attitude of three-axis stabilized communication satellites, this paper describes a novel attitude determination method using direction of arrival （DOA） estimation of a ground signal source. It differs from optical measurement, magnetic field measurement, inertial measurement, and global positioning system （GPS） attitude determination. The proposed method is characterized by taking the ground signal source as the attitude reference and acquiring attitude information from DOA estimation. Firstly, an attitude measurement equation with DOA estimation is derived in detail. Then, the error of the measurement equation is analyzed. Finally, an attitude determination algorithm is presented using a dynamic model, the attitude measurement equation, and measurement errors. A developing low Earth orbit （LEO） satellite which tests mobile communication technology with smart antennas can be stabilized in three axes by corporately using a magnetometer, reaction wheels, and three-axis magnetorquer rods. Based on the communication satellite, simulation results demonstrate the effectiveness of the method. The method could be a backup of attitude determination to prevent a system failure on the satellite. Its precision depends on the number of snapshots and the input signal-to-noise ratio （SNR） with DOA estimation.

Satellite Internet of Things:challenges,solutions,and development trends

Satellite Internet of Things(IoT)is a promising way to provide seamless coverage to a massive number of devices all over the world,especially in remote areas not covered by cellular networks,e.g.,forests,oceans,mountains,and deserts.In general,satellite IoT networks take low Earth orbit(LEO)satellites as access points,which solves the problem of wide coverage,but leads to many challenging issues.We first give an overview of satellite IoT,with an emphasis on revealing the characteristics of IoT services.Then,the challenging issues of satellite IoT,i.e.,massive connectivity,wide coverage,high mobility,low power,and stringent delay,are analyzed in detail.Furthermore,the possible solutions to these challenges are provided.In particular,new massive access protocols and techniques are designed according to the characteristics and requirements of satellite IoT.Finally,we discuss several development trends of satellite IoT to stimulate and encourage further research in such a broad area.

Coverage in Cooperative LEO Satellite Networks

Low-earth orbit(LEO)satellite networks ignite global wireless connectivity.However,signal outages and co-channel interference limit the coverage in traditional LEO satellite networks where a user is served by a single satellite.This paper explores the possibility of satellite cooperation in the downlink transmissions.Using tools from stochastic geometry,we model and analyze the downlink coverage of a typical user with satellite cooperation under Nakagami fading channels.Moreover,we derive the joint distance distribution of cooperative LEO satellites to the typical user.Our model incorporates fading channels,cooperation among several satellites,satellites'density and altitude,and co-channel interference.Extensive Monte Carlo simulations are performed to validate analytical results.Simulation and numerical results suggest that coverage with LEO satellites cooperation considerably exceeds coverage without cooperation.Moreover,there are optimal satellite density and satellite altitude that maximize the coverage probability,which gives valuable network design insights.