On the protection of fixed service receivers from the interference generated by non‐GSO satellite systems operating in the 3.7‐4.2 GHz band

In this work, the current power‐flux density limits in Article 21 of the ITU‐R Radio Regulations for non‐geostationary satellite orbit (GSO) systems operating in the 3.7‐4.2 GHz band are analyzed. These limits aim the protection of fixed service receivers, operating in the same frequency band, from the interference produced by non‐GSO satellite systems. The analysis was motivated by Resolution 157 of the World Radiocommunication Conference 2015, that recognized the need for a revision of Article 21 with a view to enabling non‐GSO systems to operate in these fixed‐satellite service frequency bands while ensuring that existing primary services are protected. In the analysis, 5 different circular Walker Delta type satellite constellation structures, adequately chosen, are considered, and the results show that the current power‐flux density (pfd) limits may impose undue constraints to non‐GSO systems operating in this band. Therefore, a methodology to investigate a more adequate pfd limiting mask is presented and used to generate an alternative mask. An evaluation of the proposed pfd mask shows that it does not impose unnecessary constraints to the non‐GSO satellite systems. This, along with other facts, indicates that the proposed pfd limits are, indeed, much more adequate than the current ones.     

低轨卫星系统频谱干扰及其规避仿真与分析

随着空间科学的发展,低轨(LEO)卫星的宽带业务需求不断增大,其使用频段向Ka等高频段扩展,不可避免地与静止轨道(GEO)卫星系统产生同频干扰.文中对GEO卫星系统受到LEO卫星系统的干扰及其规避措施进行了研究,通过建立上、下行同频干扰模型,对GEO卫星系统受到的干扰进行了仿真分析;进而,提出了基于空间隔离角和基于屏蔽...     

On the interference from space research service uplink transmissions into the inter‐satellite links of a non‐GSO system operating in the 22‐GHz band

This paper presents a compatibility analysis involving space research service lunar mission uplink transmissions and the inter‐satellite links of non‐geostationary orbit systems operating in the 22‐GHz band. Three points differentiate this analysis from the currently available studies: (1) the mathematical model used here allows for the consideration of the time varying nature of the inclination of the Moon orbital plane; (2) besides the usual unconditional interference cumulative distribution functions, this analysis also considers the conditional cumulative distribution functions given that the victim satellite is receiving interference, important to characterize the interference affecting users that, because of their location, are most of the time using satellites, which are under interference; and (3) instead of dynamic time simulation, the analytical method in Recommendation ITU‐R S.1529 is used to determine the various cumulative distribution functions involved. Four scenarios are examined in the paper. Their main differences concern the number and location of the space research service transmitting Earth stations and the strategy under which they are active (transmitting). In all scenarios, cumulative distribution functions of the ratio I/N were determined for both the in‐band and the out‐of‐band interference cases. Copyright © 2012 John Wiley & Sons, Ltd.     

In‐line interference mitigation techniques for spectral coexistence of GEO and NGEO satellites

The interest towards the deployment of Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) satellite systems in several frequency bands is increasing due to the requirement of low latency for real‐time systems and high demand of broadband data. When the number of usable Non‐Geostationary (NGEO) satellites, that is, LEO/MEO in space, increases, the frequency coexistence between the NGEO satellite systems with the already existing geostationary (GEO) satellite networks becomes a requisite. In this context, it is crucial to explore interference mitigation techniques between GEO and NGEO systems in order to allow their spectral coexistence. More specifically, in the coexistence scenario of GEO and NGEO satellite networks, in‐line interference may be a serious problem, especially in the equatorial region. In this paper, we provide several frequency sharing studies in the context of the coexistence of an NGEO satellite link with another NGEO/GEO satellite link. Furthermore, we carry out interference analysis between GEO and MEO satellite systems considering the case of the O3b satellite system and propose an adaptive power control technique for both the uplink and downlink scenarios in order to mitigate the in‐line interference. Moreover, we suggest several cognitive solutions for mitigating the in‐line interference and provide future research issues. Copyright © 2014 John Wiley & Sons, Ltd.     

Theatre in the Sky: a ubiquitous broadband multimedia‐on‐demand service over a novel constellation composed of quasi‐geostationary satellites

To meet an ever‐growing demand for wideband multimedia services and electronic connectivity across the world, development of ubiquitous broadband multimedia systems is gaining a tremendous interest at both commercial and academic levels. Satellite networks will play an indispensable role in the deployment of such systems. A significant number of satellite communication constellations have been thus proposed using Geostationary (GEO), Medium Earth Orbit (MEO), or Low Earth Orbit (LEO) satellites. These constellations, however, either require a potential number of satellites or are unable to provide data transmission with high elevation angles. This paper proposes a new satellite constellation composed of Quasi‐GeoStationary Orbit (Quasi‐GSO) satellites. The main advantage of the constellation is in its ability to provide global coverage with a significantly small number of satellites while, at the same time, maintaining high elevation angles. Based on a combination of this Quasi‐GSO satellites constellation and terrestrial networks, the paper proposes also an architecture for building a global, large‐scale, and efficient Video‐on‐Demand (VoD) system. The entire architecture is referred to as a ‘Theatre in the Sky’. Copyright © 2006 John Wiley & Sons, Ltd.     

Protection of fixed service receivers from the interference produced by the non‐geostationary satellites in a fixed satellite service network: a statistical interference analysis

Until 1997, the power flux density (pfd) limits applicable to fixed satellite service (FSS) satellite transmitters to protect fixed service (FS) receivers operating in the same frequency band were those in Article 21 of the radio regulations. They were developed assuming that potentially interfering satellites in the FSS would only operate in the GSO. The need to revise these limits to allow for the protection of FS receivers from interference generated by non‐geostationary satellites has led to several studies, most of them based on the non‐realistic assumption that every visible satellite in a NGSO constellation produces the maximum allowed pfd level at the FS receive station location. To provide a quantitative indication of how pessimistic this assumption is, this paper considers a more realistic model in which the pfd entries reaching a given FS receiver location are characterized by statistically independent random variables. The probability density functions of these random variables depend on the operational characteristics of the NGSO network. The obtained results have also shown the need to consider some of the operational characteristics of NGSO satellite networks when evaluating the interference produced by their satellites. If these operational characteristics are not taken into account in the calculations, higher values of interference, that do not reflect the real interference environment, are obtained. Copyright © 2002 John Wiley & Sons, Ltd.     

Codebook‐Based Precoding for SDMA‐OFDMA with Spectrum Sharing

This paper focuses on codebook‐based precoding for space‐division multiple access/orthogonal frequency‐division multiple access (SDMA‐OFDMA) systems aiming to guarantee high throughput for their users as well as to mitigate interference to fixed satellite service (FSS). A systematic design of SDMA codebook for subband‐based OFDMA is proposed, which forms multiple orthogonal beams with common spatial null in the direction of a victim FSS earth station (ES). The design enables both transmitter and receiver to independently construct identical codebook by sharing only on the direction angle of an FSS ES, which takes fewer overhead bits than Gram‐Schmidt process, a general method satisfying our design criterion. A system‐level throughput evaluation shows that the proposed precoding provides superior performance over existing spectrum sharing method, that is, subband deactivation. The spectrum sharing analysis shows that the proposed precoding, even with an estimation error of the direction angles of an FSS ES, causes lower interference than existing precoding, knockdown precoding.     

Semi‐distributed dynamic inter‐cell interference coordination scheme for interference avoidance in heterogeneous networks

Inter‐cell interference (ICI) is a major problem in heterogeneous networks, such as two‐tier femtocell (FC) networks, because it leads to poor cell‐edge throughput and system capacity. Dynamic ICI coordination (ICIC) schemes, which do not require prior frequency planning, must be employed for interference avoidance in such networks. In contrast to existing dynamic ICIC schemes that focus on homogeneous network scenarios, we propose a novel semi‐distributed dynamic ICIC scheme to mitigate interference in heterogeneous network scenarios. With the goal of maximizing the utility of individual users, two separate algorithms, namely the FC base station (FBS)‐level algorithm and FC management system (FMS)‐level algorithm, are employed to restrict resource usage by dominant interference‐creating cells. The distributed functionality of the FBS‐level algorithm and low computational complexity of the FMS‐level algorithm are the main advantages of the proposed scheme. Simulation results demonstrate improvement in cell‐edge performance with no impact on system capacity or user fairness, which confirms the effectiveness of the proposed scheme compared to static and semi‐static ICIC schemes.     

非静止卫星星座地球站的等效全向辐射功率包络计算方法

新兴的非静止轨道(non geo-stationary orbit,NGSO)卫星星座系统可支持分布在地球任何位置的海量地面终端,NGSO星座系统大多使用与GSO卫星星座系统同频的频段,再加上NGSO星座系统在空、时、频、码等域的高动态特性,必然会对GSO星座系统带来时变的频率干扰问题.为解决NGSO星座系统上行链路对...     

基于EPFD分析的高低轨卫星角度间隔研究

随着低轨(LEO)通信卫星业务需求的增加，低轨卫星需要使用Ka频段进行通信。本文针对低轨卫星采用Ka频段可能与在轨的高轨卫星发生同频干扰问题，采用基于链路分离角的空域分隔方法进行干扰规避的角度间隔分析。分别从不同干扰场景、地面站分布情况来分析对干扰角度间隔的影响，并在此基础上提出该角度间隔范围内，低轨卫星需采取的干扰规避措施。     

Modified methodology for computing interference in LEO satellite environments

Computing interference is very important in satellite networks design in order to assure the electromagnetic compatibility (EMC) with other radiocommunication systems. There are different methods to compute interference in geostationary (GEO) satellite systems including conventional methods using link budget equations and alternate methods such as increase in noise temperature. However, computing interference in low earth orbit (LEO) systems represents a different problem. Due to the special characteristics of this kind of orbits, the elevation angle at any site changes continuously over time, meaning a time dependent change of the propagation path length between an interfering transmitter and an interfered‐with receiver, and of the discrimination provided by the transmitting and/or the receiving antenna. Thus, conventional interference prediction methods developed for fixed links must be adapted to the case of LEO systems. To overcome this problem a mathematical model that characterizes the path length variations by an average value obtained from the probability density function of the varying distance between an interfering transmitter and an interfered‐ with receiver is proposed in this paper. This average path length enables the use of conventional link budget methods to reduce the computation time for the evaluation of interference in LEO satellite environments. Two practical examples show the possible applications of the proposed model. Copyright © 2003 John Wiley & Sons, Ltd.     

BPSK and QPSK non‐linear satellite communication system performance in the presence of cochannel interference

Taking the uplink and downlink cochannel interference and noise into account, the analytical expressions are derived for determining the bit error probability in detecting a binary phase‐shift‐keying (BPSK) and a quaternary phase‐shift‐keying (QPSK) Gray coded signal, transmitted over a satellite system exhibiting amplitude modulation‐to‐amplitude modulation (AM/AM) conversion effects and amplitude modulation‐to‐phase modulation (AM/PM) conversion effects. On the basis on the derived theoretic formulae, using real‐life system parameters, numerical results are obtained and presented. We point out the explicit comparisons of satellite communication system performance obtained when a satellite transponder amplifier is modelled by a hard‐limiter and those obtained when both AM/AM and AM/PM non‐linearities of the satellite transponder amplifier are taken into consideration. Copyright © 2003 John Wiley & Sons, Ltd.     

我国Ka频段卫星固定业务系统间干扰特性分析研究

针对我国Ka频段使用卫星固定业务的非对地静止卫星轨道（Non-Geostationary Satellite Orbit,NGSO）星座系统对对地静止卫星轨道（Geostationary Satellite Orbit,GSO）系统的干扰问题开展研究.在梳理国际电联技术建议书和《无线电规则》的基础上,通过理论分析和仿真计算等手段,对不同链路场景下NGSO星座系统对GSO系统在Ka频段的干扰问题进行分析计算.研究结果表明,在NGSO星座系统与GSO系统上下行通信有重叠部分的频段,其对GSO系统都会产生严重干扰.最后给出降低干扰的措施与建议.为我国未来拟使用Ka频段的NGSO星座系统对GSO系统的干扰分析提供参考.     

低轨大规模卫星星座系统建模与干扰分析

针对低轨(LEO)大规模卫星星座系统存在电磁空间复杂且难于观测的问题,对低轨卫星星座链路特征进行研究。以Starlink和OneWeb星座为研究对象,根据低轨卫星的星座参数,获取等效全向辐射功(EIRP)值并进行可视化处理;对获取到的低轨电磁卫星数据进行分析,获取数据的衰减特性和时间、频率等的数据关系,计算星间的链路干扰以及时间上的分布特征;获取相对干扰时间的特征值以及星间数据的衰减与时频的多维特性,并分析不同场景下的干扰时间特征,从多个维度分析低轨大规模卫星星座系统间星间链路的干扰情况并进行仿真验证。实验证明了低轨大规模卫星星座系统之间的星间链路存在干扰情况,且频率越高,干扰现象越明显。     

DS‐PAM UWB System Using Non‐linear Chirp Waveform

We propose a direct‐sequence pulse‐amplitude modulation (DS‐PAM) ultra‐wideband (UWB) system which employs a non‐linear chirp waveform instead of the conventional Gaussian monocycle in this paper. In the approved frequency for UWB, there exist myriad narrowband interferers. Specifically, we focus on the mutual interference between UWB systems and 802.11a WLAN. This paper offers a method to suppress this inband narrowband interference by introducing a kind of non‐linear chirp waveform. Using the proposed non‐linear chirp waveform, the effects of one or more narrowband interference sources with different frequencies can be suppressed. System performance of UWB systems in the narrowband interference environment can be improved. Computer simulations with additive white Gaussian noise successfully demonstrate an increase in performance with the proposed system as compared to traditional linear chirp systems.     

Multi‐group linear turbo equalization with intercell interference cancellation for MC‐CDMA cellular systems

In this paper, we investigate multi‐group linear turbo equalization using single antenna interference cancellation (SAIC) techniques to mitigate the intercell interference for multi‐carrier code division multiple access (MC‐CDMA) cellular systems. It is important for the mobile station to mitigate the intercell interference as the performance of the users close to cell edge is mainly degraded by the intercell interference. The complexity of the proposed iterative detector and receiver is low as the one‐tap minimum mean square error (MMSE) equalizer is employed for mitigating the intracell interference, while a simple group interference canceller is used for suppressing the intercell interference. Simulation results show that the proposed iterative detector and receiver can mitigate the intercell interference effectively through iterations for both uncoded and coded signals. Copyright © 2009 John Wiley & Sons, Ltd.     

Digital audio broadcasting (DAB) over non‐stationary satellite systems

Non‐stationary broadcast (BC) satellite systems can provide a continuous, direct‐to‐user, and worldwide BC service. Owing to the improved radio link margin of LEO/MEO systems, one can overcome the problems of blockage and foliage attenuation, which are significant in the alternative GEO/HEO systems. A basic analysis also reveals that the specifications of the standardized ITU A (EUREKA 147) DAB signal are adequate to cope with range and range rate effects due to the satellite motion. It is shown that a continuous, area‐wide high‐quality BC service can be provided by overlapping cellular service areas. Each cell may have an individual uplink station for feeding the BC signal. A system concept is discussed which is based on the exploitation of range, range rate, and angular information onboard the satellites with respect to each individual uplink station in order to compensate for Doppler frequency shifts and for variable signal propagation delay. Copyright © 2000 John Wiley & Sons, Ltd.     

On the performance of UNB for machine‐to‐machine low earth orbit (LEO) satellite communications

Ultra narrow band (UNB) is a widely used technology for machine‐to‐machine and low‐power wide‐area communications. Its properties, long range with small RF power, make it naturally attractive for satellite communications but also draw new challenges compared with terrestrial systems where this technology is already deployed. Indeed, the main advantage of UNB signals, their small bandwidth, makes them more sensitive to frequency drifts that are particularly present in the case of LEO satellite systems. It also implies the use of a random access method in which the carrier frequency is a parameter unknown by the receiver. In this paper, we propose a general semianalytical model to evaluate the performance of a terrestrial or satellite system using UNB technology, taking into account the multiuser interference and the frequency drift. This model is then used to assess the performance (packet loss ratio and throughput) on the return link medium access control (MAC) of a representative LEO satellite system. With our model, we analyze the effect of frequency drift on the system performance. This paper also proposes to investigate more deeply the multiuser interference modeling in order to estimate accurately the performances of a UNB system in terms of bit error rate (BER). We propose a semianalytical approach to study the interference in presence of arbitrary power imbalance that includes the effect of frequency offset and frequency drift and applicable for any linear modulation and any pulse‐shaping filter. The expression of the multiuser interference is established in the general case. We then propose a methodology to compare this exact model to the Gaussian interference approximation (mainly used through the central limit theorem) in order to assess its accuracy.     

Comparison of potential solar electricity output from fixed‐inclined and two‐axis tracking photovoltaic modules in Europe

We present an approach to determine the potential energy gains of flat plate non‐concentrating photovoltaic systems for the case of two‐axis tracking and two inclination angles with fixed orientation (assuming biannual adjustment) compared to the configuration of single fixed optimum angle. The calculation is based on the Photovoltaic Geographic Information System (PVGIS), which integrates modelling tools with the pan‐European solar radiation database. The results indicate that in the case of a PV system with two seasonal inclination angles, the maximum yearly gains, compared to the single fixed optimum angle, do not exceed 60–70 kWh per kW_p in the Mediterranean region, while in the Baltic and North Sea regions this configuration gives less than 20 kWh extra. For the case of two‐axis tracking, the relative energy gain compared to single fixed optimum angle is highest in the Northern latitudes but the absolute gain is much higher in the South. Typical yearly gains in Portugal and the Mediterranean region are in the range of 400–600 kWh per kW_p. The smallest absolute increase is found in the Northwest and Central Europe including the British Isles, where it is lower than 250 kWh per kW_p. For crystalline silicon we also investigate the effects of temperature and shallow‐angle reflectivity on the comparison between fixed and tracking systems. While both effects reduce the overall energy output, the temperature degradation is stronger for tracking systems while the reflectivity reduces output more for fixed systems. The combined effect is almost equal for fixed and two‐axis tracking systems. Copyright © 2007 John Wiley & Sons, Ltd.     

SLLR‐MDIC: Spatial log‐likelihood multiuser detection and interference cancelation scheme for OFDM‐IDMA

Wireless communication systems have gained huge attraction from research community, industrial, and academic field due to their significant impact on improving the communication efficiency, ease of deployment, and cost‐effective solution for real‐time communication. In this field of wireless communication, cellular communications have grown rapidly due to their daily usages and advantages. This increased demand of cellular communication systems has led to the evolution of 3G, 4G, and 5G communication systems, which in turn demands for higher efficiency and better bandwidth utilization. Due to heavy usage of network communication, multiple users may cause interference which subsequently may lead to the performance degradation which could be addressed using multiuser detection scheme. However, several schemes have been introduced for improving the system performance, but multiple access (MA) still remains a challenging task. Hence, in this work, we present a novel approach called Spatial Log‐Likelihood Multiuser Detection and Interference Cancelation (SLLR‐MDIC) that uses interleaving division multiple access (IDMA) to improve the communication and developed a multiuser detection approach using spatial log‐likelihood ratios. Further, we have developed orthogonal frequency‐division multiple access (OFDM)–IDMA‐based interference cancelation scheme in multiple access to improve the performance using rake receiver based approach. The performance of SLLR‐MDIC scheme is compared with existing techniques of multiuser detection in terms of bit‐error rate (BER) and symbol error rate (SER). The experimental analysis shows that proposed approach achieves improved performance when compared with existing techniques.