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Zhenwei Hou Xianqing Yi Yue Zhao 《International Journal of Satellite Communications and Networking》2019,37(3):138-148
The agility link based navigation satellite network suffers from a lack of continuous end‐to‐end connectivity. Message transmitting relies on a store‐forward mechanism—ie, data are sent from one node to another, depending on the communication opportunities, termed contacts, which arise when 2 nodes are connected by a link. To address the technical issues in such networks, the common approach is termed delay‐tolerant networking. However, the problem becomes more complicated when the message is subdivided into several frames for the limited transmission capacity of one contact. In this paper, we formalize the multiframe message broadcast problem where node may possess different knowledge, such as contact plans and message distribution, which depict the state of network and is helpful for data transmission. With the different amount of the knowledge, we investigate several different transmission strategies. And we propose the theoretical models to evaluate the above transmission strategies. Simulations prove the accuracy of our model. We also find that, as expected, the strategy using more knowledge tends to perform better. To the best of our knowledge this is the first investigation of multiframe message broadcast issues in the agility link based navigation satellite network. 相似文献
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A new protocol is proposed for reducing the power consumption of battery-powered terminals in a mobile computing environment. We exploit the fact that, in a mobile data network, mobile terminals do not continuously receive data and therefore they need not continuously operate their receivers. Nevertheless, they need to check their traffic condition periodically, that is, whether there are pending data for them or not. The proposed energy-efficient protocol is based on a paging procedure wherein a dedicated channel is used to alert (page) terminals with pending traffic. Each terminal may check its traffic condition whenever it decides to by monitoring the paging channel. The protocol is evaluated through an approximated theoretical model and through computer simulation. We focus on deriving approximate formulas for the mean message delay, the message delay variance and the power consumption. It is shown that the proposed protocol can achieve considerable power saving at a cost of increased message delivery delay. 相似文献
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《Vehicular Technology, IEEE Transactions on》1981,30(3):97-101
Potential satellite markets in the public safety (disaster relief, emergency medical, and law enforcement) and common carrier (mobile radio telephone) service areas are identified. The public mobile telephone segment is then examined to illustrate a methodology for identifying a potential satellite addressable market, including capacity requirements for roughly sizing a satellite. It is postulated that satellites could serve this lower density (mobiles per square kilometer), thin-route market at a competitive cost and thus complement terrestrial systems in the urban and more densely populated areas to provide an integrated nationwide mobile service. 相似文献
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设计了一种陶瓷基底的右旋圆极化微带天线,能够满足高温环境下卫星导航系统的应用.天线设计特点有以下四点:天线外形具有低轮廓特性, 适合高速运动飞行器表面的贴装; 采用钛合金材料和高温陶瓷材料, 能够在400 ℃高温环境下正常工作, 具有优异的耐热性能; 加工装配流程均无焊接工艺, 确保天线组件的电连接在高温冲击下的可靠性; 采用中心短路销钉设计, 减少同轴馈针的感抗, 获得优异的阻抗匹配特性.通过仿真优化和实际测试, 验证了该天线性能优异, 满足高温环境下的卫星导航系统的使用要求. 相似文献
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分析了前馈式抛物面天线和后馈式抛物面天线主要部件(如反射面、馈源喇叭、极化变换器、圆矩匹配器等)的工作原理,并讨论了天线的主要指标:增益、旁瓣特性、噪声温度和极化轴比。 相似文献
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This paper presents the design and performance analysis of a narrowband, mobile radio system optimized for dispatch-oriented broadcast applications in the 450 and 800 MHz frequency bands. The proposed system is significant since present-generation systems have proven incapable of providing the increased capacity demanded by new data services such as mobile data terminals, automatic vehicle location, and mobile facsimile. The centerpieces of the proposed design are a dynamic multiplexing technique known as packetized data, voice dedicated (PDVD) burst switching, which allows transmission of data within the silence gaps inherent in speech, and a noncausal signal processing technique called lookahead, which provides the data sources with advance knowledge of where the silence gaps will occur. Simulation results are given for two dispatch-oriented broadcast applications with widely differing traffic statistics, showing the flexibility and efficiency of the proposed system. The results show that for either application, the proposed integrated voice/data system can be retrofitted into existing 450 and 800 MHz public and private land mobile radio channels and, compared to conventional voice-only systems, can provide the user with full data services plus a tripling of voice capacity 相似文献
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A centralized, integrated voice/data radio network for fading multipath indoor radio channels is proposed and analyzed. The packets of voice and data are integrated through a movable boundary method. The uplink channel access uses a framed-polling protocol whereas the downlink uses a time-division multiple-access (TDMA) scheme. This system dynamically switches between two transmission rates and uses multiple antennas to maximize the throughput in the fading multipath indoor environment. Throughput and delay characteristics of the system are analyzed using four different techniques. The results are compared with those of Monte Carlo computer simulations. A simple relationship between the number of voice terminals and the throughput of the data traffic are derived for an upper bound of 10-ms delay for the data packets 相似文献
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A reliable one-hop broadcast is a fundamental communication primitive in mobile ad hoc networks in which a message from the source node is guaranteed to be delivered to all nodes within the source node’s transmission range. Despite the importance of it, reliable one-hop broadcast is not easy to accomplish due to collisions in wireless networks known as Hidden Terminal Problem. This paper presents a MAC protocol that not only guarantees reliable one-hop broadcast but also achieves it efficiently by exploring as many simultaneous executions of the communication as possible. In addition to the data packets, the proposed algorithm utilizes the control packets that prevent packet collisions, and at the same time, make the simultaneous communications possible to improve the network throughput. Simulation results show the effectiveness of the proposed algorithm. 相似文献
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《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1984,72(11):1611-1619
A Land-Mobile Satellite System (LMSS) is a satellite-based communications network which provides voice and data communications to mobile users in a vast geographical area. By placing a "relay tower" at a height of 22300 mi, an LMSS can provide ubiquitous radio communication to vehicles roaming in remote or thinly populated area. LMSS is capable of supporting a variety of services, such as two-way alphanumeric service, paging service, full-duplex voice service, and half-duplex dispatch service. A Network Management Center (NMC) will handle the channel requests, channel assignments, and in general the network control functions. A pool of channels is managed at the NMC to be shared by all mobile users. An integrated demand-assigned multiple-access protocol has been developed for the experimental LMSS. The pool of channels is divided into reservation channels and information channels. The information channels can be assigned by the NMC to be either voice channels or data channels. Each mobile user must send a request through one of the reservation channels to the NMC via the ALOHA random-access scheme. Once the request is received and processed, the NMC will examine the current traffic condition and assign an information channel to the user. NMC will periodically update the partitions between the reservation channels, voice channels, and data channels to optimize system performance. Data channel requests are queued at the NMC while voice channel requests are blocked calls cleared. Various operational scenarios have been investigated. Tradeoffs between the data and voice users for a given delay requirement and a given voice call blocking probability have been studied. In addition, performance impacts of such technological advancements as satellite on-board switching and variable bandwidth assignment are discussed. 相似文献
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