Transponder Channel Research Articles

On measurement noise in the European TWSTFT network

Two-way satellite time and frequency transfer (TWSTFT) using geostationary telecommunication satellites is widely used in the timing community today and has also been chosen as the primary means to effect synchronization of elements of the ground segment of the European satellite navigation system Galileo. We investigated the link performance in a multistation network based on operational parameters such as the number of simultaneously transmitting stations, transmit and receive power, and chip rates of the pseudorandom noise modulation of the transmitted signals. Our work revealed that TWSTFT through a "quiet" transponder channel (2 stations transmitting only) leads to a measurement noise, expressed by the 1 pps jitter, reduced by a factor of 1.4 compared with a busy transponder carrying signals of 12 stations. The frequency transfer capability expressed by the Allan deviation is reduced at short averaging times by the same amount. At averaging times of >1 d, no such reduction could be observed, which points to the fact that other noise sources dominate at such averaging times. We also found that higher transmit power increases the carrier-to-noise density ratio at the receive station and thus entails lower jitter but causes interference with other station's signals. In addition, the use of lower chip rates, which could be accommodated by a reduced assigned bandwidth on the satellite transponder, is not recommended. The 1 pps jitter would go up by a factor of 2.5 when going from 2.5 MCh/s to 1 MCh/s. The 2 Galileo precise timing facilities (PTFs) can be included in the currently operated network of 12 stations in Europe and all requirements on the TWSTFT performance can be met, provided that suitable ground equipment will be installed in the Galileo ground segment.

위성 중계기 특성을 감안한 OFDM 기반 위성 통신 시스템의 성능 개선

본 논문에서는 위성 중계기의 비선형 특성을 포함한 군 지연 및 이득 변동 특성을 감안하여 OFDM 기반 위성통신 시스템에 반송파 간섭 OFDM 및 채널 부호화를 적용하여 성능을 비교함으로써 개선 효과를 분석하였다. 일반적인 OFDM을 적용하는 경우와 반송파 간섭 OFDM을 적용하는 경우를 부가 백색 가우시안 잡음 환경에서 중계기의 특성과 지정된 입력 backoff 상태에 따른 BER 성능을 비교하여 성능 개선 정도를 제시하였다. 36 MHz 대역폭의 중계기 채널에 120 Mps 전송률의 정보를 16 QAM을 사용하여 전송하는 경우에 대하여 중계기의 특성이 이상적인 경우와 최악 조건의 경우로 나누어 모의실험을 적용하였다. 모의실험 결과를 통하여 중계기 내의 성능 열화에 상대적으로 심각한 영향을 미치는 군 지연과 비선형 특성에 대한 반송파 간섭 OFDM과 채널 부호화에 의한 개선 정도가 두드러지게 나타남을 알 수 있었다. 또한, 최악의 조건으로 근접할수록 적용한 채널 부호화에 의한 개선보다 반송파 간섭 OFDM에 의한 개선 효과가 더욱 커짐을 확인할 수 있었다. In this paper, the effects of performance improvement far the OFDM based satellite communications are analyzed with applying the CI(Carrier Interferometry)-OFDM and channel coding scheme considering the group delay and gain ripple characteristic as well as the nonlinear characteristic of the transponder. Comparing the BER between traditional OFDM and CI-OFDM, the degree of performance improvement is presented in AWGN channel environments for specified backoff condition of HPA. The simulations are performed with the 36 MHz bandwidth of transponder channel, 120 Mbps transmission rate, and 16 QAM modulation scheme between ideal and worst case condition. It is shown that the improvement measure by the CI-OFDM and channel coding for the group delay and nonlinear characteristic outperforms that for the gain ripple in terms of performance degradation presented by the individual characteristics. And the simulation results show that the effects of improvement by the CI-OFDM outperforms the effect by the applied channel coding, particularly in worst case condition.

Domestic and regional satellite systems

The technical characteristics of domestic and regional satellite systems are discussed. Spacecraft technology is reviewed, communication payload technology developments are discussed, and resources and economics are considered. It is seen that, compared to the installation of terrestrial microwave or optical cable networks in remote and harsh areas, satellite systems offer both lower costs and shorter time to bring on line. Proven technology and mature hardware is available for regions where orbit/spectrum space is still plentiful. As in North America, the sequence of growth is likely to be C-band and then K-band. Corresponding earth station advances in efficient modulation techniques and time-division multiple access will increase the capacity per transponder channel, while frequency and spatial reuse will provide more channels per satellite. >

CNR requirements for subcarrier-multiplexed multichannel video FM transmission in optical fibre

We clarify the CNR improvement factors applicable to FM video signals provided via satellite links employing energy dispersal waveforms, noting that a CNR of 17.5 dB is required to achieve a weighted SNR of 56 dB for a 525-line C-band NTSC signal with an energy dispersal deviation of 2.5 MHz, accommodated in a 36 MHz satellite transponder channel.

Non‐regenerative satellite switched FDMA (SS/FDMA) payload technologies

AbstractSatellite switched frequency division multiple access (SS/FDMA) satellite systems are new adaptations of the basic FDMA architecture for multiple beam spacecraft. Present multibeam satellite systems feature on‐board interbeam connections operating on a transponder channel basis, e.g. 72 MHz. SS/FDMA on board connectivity is based on much narrower channels and consequently achieves a much better utilization of spectrum resources whenever connectivity requirements are of the order of fractions of a transponder bandwidth.This work presents a critical analysis of various non‐regenerative SS/FDMA satellite systems, identifies the technological requirements to be met in order to achieve the practical realization of SS/FDMA on‐board processors and, finally, proposes two novel variable bandwidth variable centre frequency (VBVCF) demultiplexers with continuous and discrete reconfigurability.

Advanced high capacity domestic satellite communications system

This paper describes a concept of multibeam high capacity transmission possible with a 30/20 GHz and 50/40 GHz domestic satellite communication system. The relationship between satellite antenna pointing accuracy and multi-beam antenna interference, as well as the relationship between satellite antenna pointing accuracy and multi-satellite interference are looked at. The ultra high capacity domestic satellite communication system will have multi-beam antennas with a 76.0 dB at both 20 GHz and 40 GHz. These antennas will provide 4950 beams that approximately correspond to the number of end office of the Japanese telephone network, and have a pointing accuracy of 0.005 degrees. This system will be equipped with 9900 30/20 GHz and 50/40 GHz transponder channels with bit rates of 800 Mbps. Its capacity will be 119 Tbps through use of 15 large communication satellite platforms.

MSK and offset QPSK signal transmissions through nonlinear satellite channels in the presence of intersymbol interference

An expression is derived for the bit error probability of minimum shift keying (MSK) and offset quaternary phase shift keying (OQPSK) signals which have been transmitted through nonlinear satellite channels after bandlimiting. The transponder nonlinearity considered in the paper is of the bandpass type, which exhibits AM/AM and AM/PM conversion effects. The effects of up-link and down-link thermal noise are also taken into consideration in the analysis. The resulting expression for the bit error probability is an infinite series containing double integrals. In order to illustrate the usefulness of the method, the error rates of MSK and OQPSK signals are computed for a Butterworth bandlimiting filter hard limiting transponder channel model. The error rates of MSK and OQPSK signals are compared with the error rate of binary PSK signals for this communication system model.

RCA Satcom: An example of weight optimized satellite design for maximum communications capacity

The communications mission of RCA Satcom entails antenna beam coverage of all fifty states, with Hawaiian service provided by an offset spot from the primary beam for the contiguous 48 states and Alaska. To achieve minimum cost per channel in the competitive U.S. domestic market, Globcom and Alascom specified that their satellite should (1) incorporate 24 wide-band transponder channels in the commercial, 4 6 GHz band, (2) contain sufficient power and orbit control capacity to maintain all 24 channels operating continuously for a minimum of eight years, and (3) be compatible with the Delta 3914 launch vehicle, whose development they had funded jointly with the McDonnell-Douglas Astronautics Corporation at no cost to the U.S. government. This combination of requirements thus defined a communications satellite whose channel capacity is twice that of other current Delta class spacecraft but whose cost, including the launch vehicle, is significantly less than that of the corresponding 24-channel Atlas-Centaur class spacecraft designs. To meet these demands weight-optimized designs were needed in four key subsystem areas: antennas, transponder multiplexers, power supply, and attitude control as well as in the structure itself. The resultant three-axis stabilized spacecraft design with sun-oriented solar panels provides maximum power and weight capability to the primary communications payload within the launch vehicle envelope.

Dual transponder time synchronization at C band using ATS-3

The use of artificial satellites for time synchronization of geographically distant clocks has been demonstrated as early as 1962. Most techniques up to now have been plagued with one or more problems due to satellite motion, nonreciprocity of propagation, or equipment delay measurements. By using the ATS-3 satellite with its two C-band transponder channels one can avoid these problems through simple and straightforward techniques for synchronization to accuracies of tenths of microseconds. Portable cesium clocks were used to verify the accuracy of such a system.

Experience with the Applications of Radio Command Guidance to Satellite Launch Vehicles

The results of five years of experience in guiding satellites into orbit by means of radio command guidance will be described. Some flight results from the DELTA series, which includes the TIROS weather satellites; the TELSTAR, RELAY, and SYNCOM communications satellites; and various other satellites and probes will be presented and discussed.The guidance system uses a single precision monopulse radar to measure missile position and transmits corrective orders and sequencing commands to the missile, using the beam as a communications channel. The missile-borne equipment acts only as a transponder and communications channel, which gives it a considerable weight advantage over inertial systems.As a result of this experience, suitable methods for adapting the control system to handle faults in input data and in the communications path to the missile, have been determined. In addition, efficient methods for controlling radar look-angles; for limiting missile bending moments during aerodynamic phases; and reducing range safety dispersions have been developed. These techniques will be described, as well as the general methods used in applying a single guidance system and guidance computer program to such a diverse spectrum of satellite types.