摘要:

AbstractLAMS‐DLC, a data link control protocol for low altitude satellite networks, was developed to overcome throughput limitations inherent in event‐based positive acknowledgment (POS‐ACK) automatic repeat request (ARQ) class protocols by relaxing certain reliability constraints, in particular the in‐sequence delivery constraint. This relaxation results in a new class of link layer service, that of reliable datagram, and permits a fresh approach to link layer protocol design. In this paper we discuss the motivation for such a protocol, describe one such protocol, LAMS‐DLC, and compare throughput efficiency with results obtained from a simulation model. Results suggest that LAMS‐DLC provides near optimal throughput efficiencies in the target environment, while using significantly less buffer space than is required for conventional POS‐

ISSN:0737-2884    

DOI:10.1002/sat.4600120602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractRadio frequency cross‐links are the preferred communication medium for low earth orbit (LEO) satellite networks today. However, future cross‐link designs may be expected to deploy laser crosslinks to increase communication bandwidth. These cross‐links are rendered inoperative when incident with high level background radiation sources such as the Sun. The Iridium and Multiple Satellite System (MSS) are two well‐researched constellations in the literature and are ideal candidates for the investigation of solar interference on point‐to‐point constellations. In this paper a comparison of the impact of solar radiation on link availability for these two systems is presented.Evaluation of link availability based on the motions of the bodies in question is computationally infeasible. It is therefore necessary to reduce the state space to a manageable computing basis by reformulating the problem domain and by simulation. In this report the development of an algorithm and a software simulation tool to analyse the two constellations will be presented, and the results of laser cross‐link availability will be discussed. The technique introduced here may be generalized to study a variety of different c

ISSN:0737-2884    

DOI:10.1002/sat.4600120603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractAn implementation of a 16 state, rate 8/9 six‐dimensional (6‐D) 8PSK rotationally invariant trellis decoder for use in a concatenated codec is described. The concatenated codec allows transmission of STM‐1 signals (at the 155.52 Mb/s information rate) over a 72 MHz satellite transponder. The inner trellis decoder is used with an outer (255,239) RS block decoder. The trellis decoder operates at 165.93 Mb/s and currently has an implementation loss of only 0.2 dB. The concatenated codec achieves a bit error ratio of 10−10at an Eb/N0of 8.2 dB (assuming an ideal modem and AWGN channel). Details are given of many Viterbi decoding ‘tricks’ that were used in order to implement the main functions of the decoder on two 10,000 gate equivalent CMOS programmable

ISSN:0737-2884    

DOI:10.1002/sat.4600120604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractNASA Lewis Research Center is currently investigating a satellite architecture that incorporates an on‐board packet‐switching capability. Because of the statistical nature of packet switching, arrival traffic may fluctuate, and thus it is necessary to integrate the congestion control mechanism as part of the on‐board processing unit. This study focuses on the closed‐loop reactive control. We investigate the impact of the long propagation delay on the performance, and propose a scheme to overcome the problem. The scheme uses a global feedback signal to regulate the packet arrival rate of the ground stations. In this scheme, the satellite continuously broadcasts the status of its output buffer and the ground stations respond by selectively discarding packets or by tagging the excessive packets as low‐priority. The two methods are evaluated by theoretical queueing analysis and simulation. The former is used to analyse the simplified model and to determine the basic trends and bounds, and the latter is used to assess the performance of a more realistic system and to evaluate the effectiveness of more sophisticated control schemes. The results show that the long propagation delay makes the closed‐loop congestion control less responsive. The broadcast information can only be used to extract statistical information. The discarding method needs carefully‐chosen status information and a reduction function, and normally requires a significant amount of ground discarding to reduce the on‐board packet loss probability. The tagging method is more effective since it tolerates more uncertainties and allows a larger margin of error in status information. It can protect the high‐priority packets from excessive loss and fully use the down‐link bandwid

ISSN:0737-2884    

DOI:10.1002/sat.4600120605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0737-2884    

DOI:10.1002/sat.4600120606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe canonical ray tracing model of R. H. Clarke is used to validate the concept of mitigation bandwidth as used to predict DSPN spread spectrum signal variability at a mobile receiving antenna in dense scatterers. Illustrative examples of chip pulse dispersion are presented, and bit error rate performance is explored under the assumption of slow fading. The pulse dispersion is seen to pose potential obstacles to any eventual chip timing extraction and radio‐location ranging functions. Serendipitously, the performance of a DSPN embodiment of a 180° DPSK data link is seen to approximate closely that of a corresponding narrowband Rician fading link, even though no specular signal component is available to the DSPN link. The parameters of the equivalent Rician link are easily predicted from those of the DSPN li

ISSN:0737-2884    

DOI:10.1002/sat.4600120607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0737-2884    

DOI:10.1002/sat.4600120601

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY