Modeling and analysis of TCP-like multicast congestion control in hybrid terrestrial/satellite IP networks

Given their broadcast nature, satellite communications are one natural engineering choice for multicast service deployment. In this paper, the throughput performance of transmission control protocol (TCP)-like multicast congestion control is analyzed in hybrid terrestrial/satellite networks. With this objective, an analytical framework based on Markov chains is introduced. The major advantage of the proposed analytical model is its scalability in that the number of states of the Markov chain modeling the system is independent of the number of receivers in the multicast session. This is a very important feature as simulation is unfeasible for large numbers of receivers. The framework is used to evaluate the impact of the long propagation delays, high bit-error rates, and channel asymmetry characterizing hybrid terrestrial/satellite communications. The performance results show that in certain cases, it is more convenient to divide the receivers in an appropriate number of groups and establish a different multicast session toward each of the above groups. Also, the convenience of an acknowledgment (ACK) flow reconstructor is shown.     

An integrated mobile satellite broadcast, paging, communicationsand navigation system

The design of an integrated mobile satellite broadcast, paging, communications, and navigation system is described. Ku-band RadioSat ground stations will broadcast digital audio signals and data packets (including alphanumeric pages and group cells) to mobiles through a satellite to be launched in 1993. Each mobile radio will simultaneously receive L-band digital audio and data broadcasts from the satellite and L-band navigation broadcasts from the Global Positioning Systems (GPS) through a common omnidirectional mobile antenna and receiver front end. RadioSat mobile radios will use GPS broadcasts and differential corrections sent through the satellite to navigate with 2-m accuracy. With optional transmitters, RadioSat mobile radios can support two-way voice and data communications     

Modeling and analysis of applying adaptive modulation coding in wireless multicast and broadcast systems

Traditional wireless communications only utilize fixed-rate multicast and broadcast. In other words, only the most robust modulation and coding scheme can be applied for data transmission. Such a scheme fails to sufficiently exploit the potential gains of multicast and broadcast, resulting in bandwidth waste. To overcome such a problem, investigating the rate adaptation of multicast and broadcast wireless systems is the primary task. Unlike the traditional wireless systems, this paper presents an analytical model with rate adaptation for both multicast and broadcast. Adaptive modulation and coding are applied to achieve rate adaptation. We construct a stochastic model by using Finite State Markov chains for the multicast broadcast system modeling. The model’s outputs are shown to approximate to the results of our system level simulations. The model derives the performance of rate adaptation in multicast and broadcast. With the deduced modeling results, we can predict the system throughput providing the channel states, and the modulation and coding schemes variations.     

Cooperative strategies in satellite assisted emergency services

This paper deals with the cooperative strategies, which can be adopted in emergency scenarios by integrating space and terrestrial segments, and communication and localization services. First, the cooperative solutions for integrated Navigation and Communication systems are reviewed and an effective software‐defined radio implementation is described. Then, cooperative systems for broadcast and multicast communications in Incident Area Network are proposed and evaluated: in the broadcast scenario, low‐complexity relaying techniques are adopted to overcome the propagation impairments and the performance degradation; in the multicast system, radio resources management techniques for group communications are designed to allow the efficient use of scarce resources and improve connectivity and reliability of the overall system. The technical solutions have been studied and tested in the framework of the Italian National Research Project SAtellite‐assisted LocalIzation and Communication system for Emergency services [1]. Copyright © 2013 John Wiley & Sons, Ltd.     

A distributed media access protocol for packet radio networks and performance analysis. Part 1: Network capacity

A distributed time-slot assignment protocol is developed for a mobile multi-hop broadcast packet radio network, using time division multiple access channel access and virtual circuit switching. The protocol eliminates the single point failure mode of centralized network management and the delays of centralized processing. It is applicable to the user-to-user communications functions of such systems as the U. S. Army's enhanced position location and reporting system (EPLRS). The important functions of the distributed protocol, including time-slot assignment, virtual circuit set-up, and network synthesis, are identified, and implementing algorithms are presented and verified. The performance analysis of the protocol is divided into two parts. In this paper, Part 1 of the performance analysis, the capacity of a network using this protocol is studied and a tool is developed to design the network capacity by trading off among the network area, the transmission range, and the number of packet radio units. Since these results are not in closed form, numerical results provide insight into these parameters. In Part 2 the network set-up time and network data rate are analysed and a hierarchical architecture for the distributed protocol is proposed and analysed.     

Rate-Diversity and Resource-Aware Broadcast and Multicast in Multi-rate Wireless Mesh Networks

This paper focuses on the problem of increasing the traffic capacity (volume of admissible traffic) of broadcast and multicast flows in a wireless mesh network (WMN). We study and suggest routing strategies where the process of constructing the forwarding tree considers three distinct features: (a) the ability of individual mesh nodes to perform link-layer broadcasts at multiple rates, (b) the wireless broadcast advantage, whereby a single broadcast transmission covers multiple neighboring receivers and (c) the residual transmission capacity at a WMN node, subject to intereference-based constraints from existing traffic flows in its neighborhood. Our metric of interest is the total number of broadcast and multicast flows that can be admitted into the network, without resulting in unacceptable degradation in metrics such as packet loss and dissemination latency. Our discrete event simulations show that the broadcast tree construction heuristic which takes both transmission rate and residual bandwidth into account out-performs those that do not. Building on our work on resource-aware broadcast tree construction, we propose a resource-aware multicast tree construction algorithm which exploits the multiple link-layer rates, the wireless broadcast advantage and the amount of resources available. Simulation results show that this algorithm performs better than heuristics based on pruning a broadcast tree or shortest path trees.     

关于青岛市广播电视台调频广播覆盖系统的研究

青岛市广播电视台的调频广播覆盖系统是保障广播收听质量的重点内容,青岛地区广播信号所要覆盖面积较广,在3市7区内布设了7处广播基站进行同频补点。本文采用新技术、新手段,建设了网络化、智能化的调频广播编码传输系统、调频广播发射站点,并相应建设了编码传输系统和同步广播站点的监控监测平台系统,实现各个站点设备的远程监测、开路监听。该系统注重安全播出的可靠性,关键节点采用主备冗余规避了单点故障。同时,以图形、文字、音频、视频等方式直观地展示各个发射站点的每个设备的工作状态,让用户得到全方位的自动化提醒和感知,提高了维护便捷性。该系统加强了广播各套频率在偏远地区人口相对密集区域的重点覆盖,保证了收听效果,提高了覆盖范围。系统试运行以来,年故障率下降70%,覆盖范围提高10%,具有推广应用价值。     

Virtual Internet broadcasting

This article describes the design and first implementation of a virtual broadcast system whereby a multimedia content program can be edited, produced, and streamed from different locations. Data are stored and distributed decentrally, allowing multiple combinations of program objects to new programs. The virtual broadcast station is the network. This concept additionally offers the clients the opportunity to obtain an individual (personalized) program, still using bandwidth-economic multicast technologies. This is achieved by dividing multimedia streams into temporal chunks (chunk streams), streamed over different multicast host groups (distributed multicasting), using existing Internet session control protocols (SDP) and Internet transport protocols (RTP). A client application assembles the transmitted chunks to form an individual program. This technique can also be used to insert personal/local advertisements into broadcast-like services     

Network Bandwidth Requirements for Scalable On-Demand Streaming

Previously proposed streaming protocols using broadcast or multicast are able to deliver multimedia files on-demand with required server bandwidth that grows much slower than linearly with request rate, or with the inverse of client start-up delay. The same efficiencies can be achieved for network bandwidth if delivery is over a true broadcast channel. This paper considers the required network bandwidth for on-demand streaming over multicast delivery trees. We consider both simple canonical delivery trees, and more complex cases in which delivery trees are constructed using both existing and new algorithms for randomly generated network topologies and client site locations. Results in this paper quantify the potential savings from use of multicast trees that are configured to minimize network bandwidth rather than the latency to the content server. Further, we determine the network bandwidth usage of particular immediate service and periodic broadcast on-demand streaming protocols. The periodic broadcast protocol is able to simultaneously achieve close to the minimum possible network and server bandwidth usage.     

硬盘播出系统的发展及应用

硬盘播出系统是一种全新的广播电视播出系统,与传统的磁带播出系统相比具有显著的优点,它提高了系统的可靠性,使节目编排灵活方便,安全性和播出质量都显著提高.只要解决好节目源的硬盘化,系统就能升级为全自动的硬盘播出系统,它是广播电视播出的发展方向.     

电台节目资源库素材收录与转换实践

广播电台要达到良好的播出效果,必须从制播的源头即节目素材源就开始把好质量关.从广播录制技术质量标准出发,阐述了广播节目的采样率、位数和码流等技术指标特性;同时,针对海量广播素材如何标准化导入音频工作站系统的难题,介绍了作者在电台工作实践中为此所做的技术革新.     

Broadcast analysis and prediction in the HF band

A comparative study of the commonly used methods for the prediction of the coverage area due to a transmitter operating in the HF band is presented. Those statistical model based tools are: ITU Rec. 533, Ionospheric Communication Analysis and Prediction Program; IONCAP, Voice of America's VOACAP and Ionospheric Communication Enhanced Profile Analysis and Circuit Prediction Program; ICEPAC. The received signal due to a typical transmitter located at Cricklade, England, operating around 7.9-19.1 MHz (HF band I) is computed as a function of frequency, time and the sunspot number. The ray tracing method calculates the virtual height, the calculated results are compared with the experimental data and the discrepancies are examined     

Throughput analysis of tandem-type go-back-N ARQ scheme forsatellite communications

The tandem-type go-back-N (GBN) scheme has been proposed for satellite communications to reduce the long roundtrip delay using the onboard processing of satellites. The author considers the exact analysis of the throughput performance of this scheme and its application to a broadcast communications system such as a point-to-multipoint file transfer system. First, the throughput expression for the point-to-point tandem-type GBN scheme is derived. Second, applying the results of this point-to-point tandem-type GBN scheme to a broadcast (point-to-multipoint) communications system, the relationship of the number of receiving stations to the link bit error rate and the roundtrip propagation delay is shown     

A methodology for modeling the reliability, availability andmaintainability (RAM) of a generic shortwave broadcast relaystation

A methodology for developing a reliability, availability and maintainability (RAM) model that is applicable to evaluating conceptual designs for shortwave broadcast relay stations is described. A generic relay station (GRS) that has nine major subsystems exclusive of ionospheric propagation path is proposed. The reliability of the propagation path to the listeners is not addressed. An example of the use of the methodology is presented for the GRS and the sensitivity of the model results is studied for the most significant subsystems from a RAM standpoint: the satellite earth station that delivers the program feeds and the high-powered transmitters     

A semi empirical model for low latitude HF ionospheric propagationprediction

The ionospheric propagation of high frequency (HF) radio waves is strongly dependent on the varying structure of the ionosphere. It is therefore essential to look for an accurate and suitable physical model for the design and development of telecommunication links, especially broadcast links, which are affected by such variation. This enables the prediction of radio link performance with a satisfactory level of accuracy and reduced computation time. Existing models make extensive use of powerful computers to generate electron density profiles, whereas this model attempts the same on an 80486 based PC successfully. Though this affects the accuracy of the generated profiles, it is still acceptable for engineering applications. A physical model of the ionosphere is developed with empirical additions from rocket data. The associated propagation conditions are simulated and the results compared with practical data obtained from broadcast and amateur radio band usage. A high degree of correlation is obtained     

Performance analysis of geography‐limited broadcasting in multihop wireless networks

In multihop wireless networks, delivering a packet to all nodes within a specified geographic distance from the source is a packet forwarding primitive (geography‐limited broadcasting), which has a wide range of applications including disaster recovery, environment monitoring, intelligent transportation, battlefield communications, and location‐based services. Geography‐limited broadcasting, however, relies on all nodes having continuous access to precise location information, which may not be always achievable. In this paper, we consider achieving geography‐limited broadcasting by means of the time‐to‐live (TTL) forwarding, which limits the propagation of a packet within a specified number of hops from the source. Because TTL operation does not require location information, it can be used universally under all conditions. Our analytical results, which are validated by simulations, confirm that TTL‐based forwarding can match the performance of the traditional location‐based geography‐limited broadcasting in terms of the area coverage as well as the broadcasting overhead. It is shown that the TTL‐based approach provides a practical trade‐off between geographic coverage and broadcast overhead. By not delivering the packet to a tiny fraction of the total node population, all of which are located near the boundary of the target area, TTL‐based approach reduces the broadcast overhead significantly. This coverage‐overhead trade‐off is useful if the significance of packet delivery reduces proportionally to the distance from the source. Copyright © 2011 John Wiley & Sons, Ltd.     

Medium wave skywave beams

The author discusses the advantages and drawbacks of skywaves and why they are avoided by domestic medium-wave broadcaster. He reports some results of a computer investigation of problems encountered with medium-wave antennas coupled to a skywave propagation medium. Experimental results are given showing skywave patterns for broadcasts from Alaska, one using a horizontal and the other a vertical antenna. It is concluded for these two examples that remarkable medium-wave coverage could be obtained using available frequencies     

简易硬盘播出系统的设计

采用简易硬盘播出系统来控制电视节目的播出,可有效解决小型电视台以及单位闭路电视系统播放新闻及VCD、DVD等盘片节目的需求,其优点是节目一次加载完成后,通过计算机计划任务程序的控制来实现节目无人值守自动播出,能节省大量的人力.     

Low-Latency Broadcast in Multirate Wireless Mesh Networks

In a multirate wireless network, a node can dynamically adjust its link transmission rate by switching between different modulation schemes. In the current IEEE802.11a/b/g standards, this rate adjustment is defined for unicast traffic only. In this paper, we consider a wireless mesh network (WMN), where a node can dynamically adjust its link-layer multicast rates to its neighbors, and address the problem of realizing low-latency network-wide broadcast in such a mesh. We first show that the multirate broadcast problem is significantly different from the single-rate case. We will then present an algorithm for achieving low-latency broadcast in a multirate mesh which exploits both the wireless multicast advantage and the multirate nature of the network. Simulations based on current IEEE802.11 parameters show that multirate multicast can reduce broadcast latency by 3-5 times compared with using the lowest rate alone. In addition, we show the significance of the product of transmission rate and transmission coverage area in designing multirate WMNs for broadcast     

Understanding and Exploiting the Trade-Offs between Broadcasting and Multicasting in Mobile Ad Hoc Networks

We find that current group communications protocols are far from "one size fits all", they are typically geared toward and optimized for particular scenarios. Multicasting, in general, works well if the density of group members is sparse and in low mobility; broadcasting, in contrast, works well with a high density of group members and in high mobility. Due to the dynamics of the network, one strategy may be preferable to the other at different times and in different localized regions. In this paper, we first quantify the trade-offs between broadcasting and multicasting and evaluate the suitability of a strategy in various scenarios of deployment. Based on the lessons learned, we design a protocol that adapts in response to the dynamics of the network. We named our protocol Fireworks. Fireworks is a hybrid two-tier multicast/broadcast protocol that provides efficient and lightweight multicast dissemination and self-adapts in response to variations in the density and distribution of group members to provide efficient performance. Fireworks creates pockets of broadcast distribution in areas with many members, while it creates and maintains a multicast backbone to interconnect these dense pockets. Fireworks offers packet delivery statistics comparable to that of a pure multicast scheme but with significantly lower overheads. We also show that Fireworks has a lower level of degrading influence on the performance of coexisting unicast sessions than either traditional multicast or broadcast methods