Showing papers on "Telecommunications link published in 1983"

Method and apparatus for graceful preemption on a digital communications link.

Abstract: A method and apparatus for preemption on a digital communications link (51) used for selective communication by a plurality of user devices (10, 11). When a first user device is actively communicating over the link, a second user device can preempt the first user device by having a link controller (1000) transmit a preempt character. The link controllers at either end of the link each save values of a set of status variables collectively defining the status of the link controller. When the second user device relinquishes link access, the saved values are used to return the link controllers to their status at the time of preemption such that the first user device can resume communication from the point of interruption without requiring data retransmission.

Minimum-shift keyed modem implementations for high data rates

Abstract: IGITAL communications links capable of conveying data at hundreds of megabits per second (Mb/s) are becoming increasingly important in various applications. An example is the use of time division multiple access (TDMA) transmission through a satellite relay wherein several data channels are routed through single uplink and downlink paths (antenna beams). Separation of the channels from each other is accomplished through interleaving and deinterleaving in time, with possible rerouting taking place in the satellite. When carrying traffic from large metropolitan areas, the required data rates can exceed 100 Mb/s. One such implementation, currently under study by NASA,' involves data transmission at rates of up to 550 Mb/s. Such applications require the use of modulation schemes that use the available bandwidth efficiently. Furthermore, because power is at a premium on board a satellite, the utmost in power efficiency is desired of the chosen modulation scheme. This implies the use of a constant-envelope modulation scheme since amplifiers, such as traveling wavetube amplifiers, are most efficient when operated near saturation. Three popular constant-envelope modulation schemes for efficient transmission of digital data are quadriphase-shift keying (QPSK), offset (or staggered) quadriphase-shift keying (OQPSK), and minimum-shift keying (MSK). Two excellent recent articles [1,2] in IEEE Communications Magazine have discussed their general properties and attributes as well as those of other modulation schemes with constant (or nearly constant) envelopes. Other recent papers [3-61 have presented analytical results and computer

A Multibeam Packet Satellite Using Random Access Techniques

Abstract: The performance of a multibeam packet satellite using ALOHA type random access techniques is studied. The satellite provides either no buffer or an infinite buffer for successful packets on the uplink channels. A TDMA frame is organized in accordance with the traffic demand from each area. System throughput and packet delay have been successfully obtained. Aiming at improving the performance of the system, three different protocols are introduced and studied in the zero buffer case. It is demonstrated, through examples, that satisfactory system performance can be obtained using an appropriate protocol. However, system performance can also be severely degraded if the transition time for the satellite transponder to switch from one zone to another is not negligible. In this case, the performance can be restored via the use of a buffer of sufficiently large size.

Multiple downlink data aggregator and system

Abstract: In a TDMA satellite communications system with a plurality of transponders and a network of satellite communication controller (SCC) terminals, a data aggregator which may be attached to a local SCC. The data aggregator simultaneously receives TDMA frames from at least two transponders and aggregates locally addressed traffic channels into a TDMA pseudo-frame for delivery to the SCC.

The Deep Space Network: A Radio Communications Instrument for Deep Space Exploration

Abstract: The primary purpose of the Deep Space Network (DSN) is to serve as a communications instrument for deep space exploration, providing communications between the spacecraft and the ground facilities. The uplink communications channel provides instructions or commands to the spacecraft. The downlink communications channel provides command verification and spacecraft engineering and science instrument payload data.

Closed-Loop Transmitting Power Control System for K-band Satellite Communications

Abstract: In order to cope with K-band link loss variations and also to improve link reliability, a new closed-loop satellite access power control system is proposed. This system controls Earth station transmitting power so that the overall satellite link quality, such as S/N or error rate, converges to the stipulated value. Satellite transmitting power is also optimized by this control, enabling a considerable increase in transmission capacity and improvement in link reliability.

An Integrated Design Approach to 30/20 GHz Trunking Systems

Abstract: A design procedure for 30/20 GHz trunking systems is presented which permits the joint optimization of the satellite links and the terrestrial links between diversity terminals of individual earth stations. This process involves the generation of uplink and downlink power control functions (PCF's), which depend on 1) the rapidity with which power control can be exercised, relative to the rate of variation of atmospheric attenuation, and 2) the available uplink and downlink HPA power. The PCF's combine to produce a link availability curve (LAC), which describes the uplink/downlink fade combinations for which a specified bit error rate (BER) can be maintained. The set of required terminal separation distances (TSD's) can generally be computed from the LAC, together with the marginal uplink and downlink attenuation distributions. Methods of implementing uplink and downlink power control are discussed. In particular, several alternatives for determination of uplink attenuation and selection of the appropriate transmit terminal are contrasted.

Millimeter Wave Advantages for Satellite Communications

Abstract: Recent gaseous attenuation relations are combined with a 1980 Crane rain attenuation model to give total atmospheric attenuation versus frequency in Florida. This attenuation model is used to find optimum satellite uplink frequency estimates in a crowded commercial environment. The 20-40 GHz region is attractive for maximum signal/ interference on the uplink for modest availability. Downlink performance is then examined: a 40+ GHz spot beam to New York offers excellent signal/ interference from a crowded geostationary arc.

Improvement of K‐band satellite link transmission capacity and availability by the transmitting power control

Abstract: To cope with the rain attenuation in K-band (quasi-millimeter waveband) satellite communication, the effect of a transmitting power control scheme which controls adaptively the onboard transponder transmitting power toward each earth station according to the downlink rain attenuation, is clarified quantitatively. Also, the design of the FDMA satellite communication system with transmitting power control is made possible. Probability distribution of the downlink rain attenuation is used to represent each FDMA carrier transmitting power. the total transmitting power of the transponder is obtained as the sum of these FDMA carrier powers by using the central limit theorem. By the probability density function of this total power and the upper limit of this total power which is determined by the transponder maximum transmitting power and the output backoff, the maximum allocatable FDMA channels per transponder is derived. Further, the channel capacity of the overall system is calculated, taking account of rain attenuation distribution, regional differences of satellite antenna gain, and regional distribution of earth stations. By these procedures, the allocatable number of channels and the link availability are derived, and the design of the FDMA satellite communication systems with transmitting power control is made possible. As an example, considering Japanese CS-2 satellite, the number of channels and link availability for 64 Kbps and 1.544 Mbps earth stations with antenna diameter 3 mo, are shown.

Estimating Signal Suppression under Hard-Limiting

Abstract: This paper presents methods for determining small signal suppression as signals pass through a hard-limiter. Methods presented will be useful to the systems engineer who wishes to obtain a network power balance for satellite communications networks supported by a hard limited satellite transponder. This class of problem requires the calculation of suppression on satellite links numbered in the hundreds. Therefore speed of calculation becomes important. The key feature of the methods presented is their adaptability to a small desk-top computer and their reduction of processing time.

Precision phase comparison via communication satellites using loop‐back tones

Abstract: Phase comparison of remote oscillators by tone transmission via communication satellites is considered. By introducing loop-back tones at each station to produce a virtual downlink frequency equal to the uplink frequency, the path phase between two stations is made independent of the direction of transmission. All nondispersive path effects are then canceled by using reverse path transmissions. The effective period for phase comparison is the mean period of the uplink and downlink transmissions. This represents a 2–order of magnitude increase in effective frequency over the previously used two-tone method. The precision of phase comparison via satellites is now limited by uncertainties of ionospheric effects.

Telecommunications performance analysis and monitoring software

Abstract: Jet Propulsion Laboratory flight projects and the Deep Space Network require accurate prediction of telecommunications link capability Link capability determines spacecraft command message error rate, science data telemetry error rate, and radiometric angle, velocity, and position errors during a mission To establish link performance capability, the analyst commonly translates these error rates into corresponding signal-to-noise ratios or received signal power levels To validate predicted capability, the analyst compares actual (measured) signal-to-noise ratios or signal levels with previously predicted values for the same link configuration and time

The prediction of weather effects on telecommunications link performance

Abstract: This chapter presents a theoretical model which combines the statistical description of communications link performance [9-1] with a statistical description of weather effects. The measured effects of weather, namely atmospheric attenuation and increase in ground receiver system noise temperature, are additive (in decibels). The combined probability density function is therefore the convolution of the separate density functions.

Frequency Tracking a Downlink FH Signal for Mobile Platforms

Abstract: A mobile platform receiving a frequency hopped (FH) downlink must acquire and track that link to sustain communications. A technique originated by Ziv and Zakai allows us to lower bound the achievable frequency error for a variety of channel conditions (Gaussian, partial-band, Raleigh). In closed loop space-to-ground tracking systems which have an FH uplink as well, frequency precorrection may be needed on each of the terminal's transmissions. The frequency error model developed in this paper is used in combination with models of other frequency error sources to yield analysis that can aid in selecting tracking update rates.