Future Satellite Communication Systems Research Articles

On‐board large mesh antenna reflector with high surface accuracy

AbstractAn increase in the size of on‐board antenna reflectors is a key technology in providing economical services by miniaturized portable equipment in future mobile satellite communication systems. In practice, a mesh antenna can be used as the on‐board antenna. However, since the reflector surface of this antenna is supported by the cable and the mesh, and its size is larger, the surface is subject to larger thermal deformation in orbit than is the solid antenna reflector. Conventional compensation methods such as passive thermal control or rotation of the antenna reflector cannot maintain the required antenna performances. Various methods have been reported to compensate for the deterioration of antenna performance by thermal deformation.This paper describes a static shape control system for a 10‐m diameter antenna which actively compensates for the deformation by using a shape‐measuring sensor and shape‐compensation actuator. The configuration of the sensor and the experimental results by a functional model are described to confirm the design validity. The shape‐compensation method by the actuator was confirmed to be useful in achieving a required surface accuracy.

A future satellite communications system using millimetre‐wave bands and an on‐board processor

AbstractThis paper proposes the system concept of a personal satellite communications system that will be available in the first decade of the 21st century. Technologies of millimetre‐wave bands and an onboard processor with baseband switching promise to meet the requirements of a personal communications system: portability, low‐cost, and large capacity. Based on the prospects of these technologies, the most likely parameters for the future personal satellite communications system and the configuration of a suitable on‐board processor are proposed. A trial model of such an on‐board processor has been made. In this paper, details of the trial model on‐board processor and its future developments are described.

Transmission of SDH signals through future satellite channels using high-level modulation techniques

The authors discuss the possibility of transmitting synchronous digital hierarchy (SDH) signals through two-link nonlinear satellite channels. Transmitting such high bit rate signals through a standard 54 MHz or 36 MHz transponder bandwidth requires the use of high-level modulation schemes. The techniques and technologies needed to make the use of 16-ary quadrature amplitude modulation (QAM) and 64-ary QAM transmissions feasible for future satellite communication systems are examined. It is shown that it is possible to transmit a synchronous transport module-level 1 (STM-1) signal through a standard 54 or 36 MHz transponder bandwidth using 16-ary QAM or 64-ary QAM transmission, respectively, for the 6/4 GHz band. However, for higher frequency bands, due to high fade margins needed to achieve the high availability and performance for SDH systems, is not practical to transmit the STM-1 signal through such standard transponder bandwidths.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modems for emerging digital cellular-mobile radio system

Digital modem techniques for emerging digital cellular telecommunications-mobile radio system applications are described and analyzed. In particular, theoretical performance, experimental results, principles of operation. and various architectures of pi /4-QPSK ( pi /4-shifted coherent or differential QPSK) modems for second-generation US digital cellular radio system applications are presented. The spectral/power efficiency and performance of the pi /4-QPSK modems (emerging American and Japanese digital cellular standards) are studied and briefly compared to GMSK (Gaussian minimum-shift keying) modems (proposed for European DECT and GSM cellular standards). Improved filtering strategies and digital pilot-aided (digital channel sounding) techniques are also considered for pi /4-QPSK and other digital modems. More spectrally efficient modem trends for future cellular mobile (land mobile) and satellite communication system applications are also highlighted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Digital signal transmission characteristics in maritime satellite communications

AbstractDigital signal transmission will be used widely in the future mobile satellite communication system to realize an efficient operation of the system and to provide diversified service. In the global mobile satellite communication system, such as maritime and aeronautical communications where a wide service area is required, the influence of the multipath fading due to sea surface reflection at low elevation angle on the digital signal transmission characteristics is a particular problem.This paper deals with the application of the digital transmission system to the INMARSAT (International Maritime Satellite Organization), which provides the international maritime satellite communication service. The configuration of the digital maritime satellite communication system, which was developed for experimental purpose, as well as the result of analysis of the digital signal transmission characteristics in the low‐elevation maritime communication experiment, are presented.Based on the result of field experiment, the required power margin for low elevation operation is evaluated, and a means to secure a high‐quality communication is discussed. Thus, a guideline is presented for the digital transmission system design in mobile satellite communication, affected by the sea surface multipath fading.

Performance study of 16‐ary deqam modem for future satellite communication systems

AbstractThis paper investigates the effects of additive white Gaussian noise (AWGN), adjacent‐channel interference (ACI) and co‐channel interference (CCI) combined with flat fading on the performance of bandlimited 16‐ary differentially encoded quadrature amplitude modulation (16‐ary DEQAM) signalling transmitted through a non‐linear high‐power amplifier (HPA). It is assumed that the HPA exhibits both AM‐AM and AM–PM conversion distortions. This situation may be applied to the up‐link or down‐link of a regenerative satellite system where the HPA is the earth‐station travelling‐wave tube (TWT) or the on‐board TWTA, respectively. The signal‐to‐noise ratio (SNR) degradations at a specific bit error rate (BER) are evaluated by means of a series of computer simulation tests for various values of channel roll‐off factor α (channel bandwidth) and different degrees of output backoff (OBO) of the HPA in the presence of various combinations of the channel impairments. It is shown that by employing a baseband or RF predistortion technique for the HPA and selecting the best arrangement of channel roll‐off factor, OBO value of the HPA and channel spacing, a good performance can be achieved regarding the most efficient use of bandwidth together with a minimum SNR degradation due to the presence of channel impairments. Thus, the use of 16‐ary DEQAM for satellite communications is feasible in the near future.

Review of SHF and EHF slant path propagation measurements made near slough (UK)

Studies of the effects of the atmosphere on radiowave propagation relevant to the planning and operation of future satellite communication systems at frequencies above 10 GHz have been carried out at Slough for over ten years. Observational data, which relate mainly to attenuation by rain and cloud, are available within the band 11 to 110 GHz. With reference to systems performance, this paper reviews the results on atmospheric attenuation derived from single-site and space diversity experiments involving fixed-pointing radiometers, sun-tracker radiometers and test transmissions from the ATS-6, OTS and SIRIO satellites. The latter have also enabled information to be obtained on depolarisation by atmospheric constituents with particular reference to frequency reuse applications.

MILSATCOM Architecture

The Military Satellite Communications Systems Office (MSO) of the Defense Communications Agency has recently prepared an architectural framework for the evolution of military satellite communications systems through the end of this century. The realization of the goals of the architecture should provide significantly enhanced military utility to three functional classes of users. The strategic forces would be directed and managed through a two-way, highly survivable, jam-resistant Strategic Satellite System (SSS). The Tactical Satellite System (TACSATCOM II) offers a jam-resistant, low probability of detection, communications system for employment of ground mobile forces as well as tactical Naval and Air Forces. The future Defense Satellite Communications System (DSCS III U/IV) will provide the high data-rate users with increased jam resistance to perform their missions. These satellite systems will use higher frequency bands (EHF), on-board processing, and improved antenna techniques. To implement the EHF technology in a coherent fashion, the MSO has also prepared a Technology Development Program Plan which identifies and plans for the needed R&D efforts.

Comstar Experiment: An Overview of the Bell Laboratories 19- and 28-GHz Comstar Beacon Propagation Experiments

Radio beacons on the COMSTAR communication satellites transmit continuously at 19 and 28 GHz to permit the long-term measurement of the properties of earth-space propagation needed in designing future high-capacity satellite communication systems. An extensive receiving facility has been established at Crawford Hill, New Jersey, for measuring attenuation, depolarization, coherence bandwidth and scatter of the beacon signals by atmospheric processes. The facility includes a precision 7-meter antenna and multichannel receiving electronics designed to obtain optimum benefit from the COMSTAR beacons. Other Bell Laboratories receiving facilities in Georgia and Illinois are accumulating statistics on signal attenuation and diversity improvements for other climatic conditions.

Satellite communications in the 1980s and after

The second decade of satellite communications which we are now entering should show as rapid progress as the first, which saw the creation of a global network of satellites and Earth stations connecting eighty countries on six continents. Domestic systems are providing many types of services to small and large communities, and maritime systems to ships at sea. Future satellite communications systems will have higher capacity and provide varied services to small users. Increased transmission of television, graphics, and computer data will be provided, interconnecting individual users with ‘rooftop’ and mobile terminals. Technological advancements in this second decade will involve the use of new frequency bands (30/20 and 14/11 GHz), and frequency reuse through spatial separation and polarization discrimination. Digital transmission techniques will find widespread use. The third decade will see the application of very large multibeam, multifrequency antenna systems, beam shaping, and satellite onboard switching and processing. The use of the space shuttle with high-energy upper stage propulsion units will allow the deployment of very large, permanent geostationary platforms for providing economical multiple communications service.

Proposal of QAM-OFDM System with IDAR Method Designed for Satellite Channel

The future satellite communication systems are required to support the higher transmission data rate for providing multimedia services by employing the efficient modulation method such as multilevel QAM. However, the employment of conventional single carrier transmission method with multi-level QAM which has larger PAPR (Peak to Averaged Power Ratio) would cause the fatal degradation of signal quality due to the non-linear amplifiers located at the earth station and satellite. To overcome this problem, this paper proposes broadband satellite communication systems by using the multilevel QAM-OFDM technique with IDAR (Improved Decision Aided Reconstruction) method, which is designed for satellite channel. In the IDAR method, the characteristics of non-linear amplifiers are required to be known at the receiver for mitigating the intermodulation noise. This paper also proposes the estimation method for AM-AM and AM-PM conversion characteristics of non-linear amplifiers by using low PAPR preamble symbols. The various computer simulations are conducted in this paper to verify the effectiveness of proposed system in the non-linear satellite channel.

Mitigation of Non-linear Distortion Using PTS and IDAR Method for Multi-Level QAM-OFDM System

The future satellite communication systems are required to support the higher transmission data rate for providing the multimedia services by employing the efficient modulation method such as multi-level QAM. The employment of single carrier transmission with multi-level QAM would cause the fatal degradation of signal quality due to the non-linear amplifiers located at the earth station and satellite. To overcome this problem, we have proposed the multilevel QAM-OFDM technique with IDAR (Improved Decision Aided Reconstruction) method designed for non-linear satellite channel. However, the proposed method could not mitigate the non-linear distortion sufficiently when modulation level becomes higher such as 64QAM. This paper proposes the combined scheme of partial transmission sequence (PTS) and OFDM-IDAR methods so as to enable the usage of higher multi-level QAM method, which can achieve the higher transmission data rate with keeping the better bit error rate performance in the non-linear satellite channel. The various computer simulations are conducted in this paper to verify the effectiveness of proposed method in the non-linear satellite channel.

All-Weather Earth Station Satellite Communication Antennas

The successful TELSTAR® and Relay satellite experiments have led to consideration of the equipment and techniques that might be incorporated in future commercial and military satellite communication systems.