Broadcast delivery

The architecture and performance of systems that use a broadcast channel to deliver information to a community of users are discussed. Information is organized into units called pages, and at any instant of time, two or more users may request the same page. Broadcast delivery is attractive for such an environment because a single transmission of a page will satisfy all pending requests for that page. Three alternative architectures for broadcast information delivery systems are considered. They are one-way broadcast, two-way interaction, and hybrid one-way broadcast/two-way interaction. An important design issue is the scheduling of page transmissions such that the user response time is minimized. For each architecture, existing scheduling algorithms are described, and their mean-response-time performance evaluated. Properties of scheduling algorithms that yield optimal mean response time are discussed. A comparative discussion of the performance differences of the three architectures is also provided     

Response Time in a Teletext System: An Individual User's Perspective

Teletext is a one-way, broadcast-delivery information system. Pages of information are continuously broadcast to the users. User terminals monitor the broadcast stream and requested pages, once recognized, are captured and stored. Teletext systems possess many attractive features. Among them are simplicity of operation and insensitivity of system performance to user loads. Previous research has considered the issue of response time optimization in teletext systems. In those studies, response time was averaged over the entire user population. In this paper, we analyze an individual user's response time experience. Needless to say, this provides a better gauge of the quality of service being delivered. In addition, this perspective provides the appropriate framework for evaluating strategies that take advantage of user terminal storage capabilities to improve response time performance. To demonstrate this, one such strategy is developed and analyzed. Numerical examples that illustrate the use of the paper's results are also presented.     

Theory and methods for design of pulse shapes for broadcastteletext

The theoretical and practical engineering constraints, considerations, and methods for pulse shape design for North American broadcast teletext transmissions are described. The principles and concepts described are for broadcast over-the-air transmission, but they are also applicable to satellite and cable transmission of broadcast teletext signals. Overall objectives of pulse shape design are summarized. Basic constraints and considerations from the Nyquist theory are described. The practical and engineering constraints on teletext pulse shapes are discussed in detail. Pulse shape apportioning and specification are treated. A critical review is provided of the theory and design methods for teletext pulse shaping. A review of analytical and numerical approaches is given. Modelling and simulation approaches are described, including novel comprehensive model. Improved overall and transmitted pulse shapes are evaluated and their performance compared to that obtained with other common pulse shapes     

Real time teletext broadcast system performance enhancement usingghost rows

Teletext is a one way broadcast system which provides a variety of services to its users. A one way broadcast system is attractive because a single transmission of a piece of information satisfies all potential users of that information. The main drawback of these types of systems is that a user must wait until the required information arrives. Therefore, the access time is an important consideration in the design of broadcast teletext systems. In addition, another important factor, information update delay, is very significant in real time broadcast teletext. The shortening of this delay is important for real time applications especially for systems broadcasting financial information. In this paper, we propose to use the ghost rows together with the storage capabilities of modern terminals to shorten both the access time and the update delay. A queueing model is developed to analyse the performance of this new system     

Extraction of teletext channel information from measured complexand in-phase impulse responses at baseband and their significance

The technical advantages of measuring complex impulse responses rather than the in-phase component of broadcast teletext channels and the extraction of channel information from real impulse response measurements and its limitations are described. A number of illustrative examples are provided. It is concluded, after discussion, that measurements of channel complex impulse responses are necessary, in spite of extra cost, so that suitably flexible and general computer simulation design and performance studies of broadcast teletext systems can be made     

Response Time Performance of Videotex Systems

Videotex is an interactive information system which provides a variety of services to its users. Examples of such services are information retrieval, software distribution, transaction processing, and message handling. An important aspect of the quality of service experienced by a videotex user is the response time. We consider the use of mixed individual/broadcast delivery to enhance the response time performance. Broadcast delivery is attractive for information retrieval applications where several users may be requesting the same information page, and a single broadcast of this page will satisfy all requests simultaneously. Individual response, however, is required for transaction-oriented services and for the retrieval of confidential information. A queueing model is developed to study the performance of videotex systems under mixed delivery. Analytic results are derived for the mean response time. Numerical examples are presented to show the performance characteristics of mixed delivery, and how it can be used to enhance the response time performance without increasing the processing capacity of the system.     

用UML设计通用DVB图文电视处理组件

提出了一种针对DVB图文的终端软件解决方案,介绍了该方案基于UML技术的建模设计过程,分析了解码,存储,导航等关键功能,提出了操作系统抽象和回调处理页面显示的思想,解决了组件的兼容性和可移植性问题,最终完成了一个可被广泛集成的通用图文处理组件.     

Performance evaluation of a teletext system

Four parameters are defined to measure the performance of a teletext system, namely, the probability of delivering a message within specified time, the transmission efficiency, the average number of errors per page, and the throughput. Each of them is derived and computational results are presented taking the UK teletext system as an example. These parameters are compared in their ability to characterize the performance of the teletext system     

Efficient algorithms for scheduling data broadcast

With the increasing acceptance of wireless technology, mechanisms to efficiently transmit information to wireless clients are of interest. The environment under consideration is asymmetric in that the information server has much more bandwidth available, as compared to the clients. It has been proposed that in such systems the server should broadcast the information periodically. A broadcast schedule determines what is broadcast by the server and when. This paper makes the simple, yet useful, observation that the problem of broadcast scheduling is related to the problem of fair queueing. Based on this observation, we present a log‐time algorithm for scheduling broadcast, derived from an existing fair queueing algorithm. This algorithm significantly improves the time‐complexity over previously proposed broadcast scheduling algorithms. Modification of this algorithm for transmissions that are subject to errors is considered. Also, for environments where different users may be listening to different number of broadcast channels, we present an algorithm to coordinate broadcasts over different channels. Simulation results are presented for proposed algorithms.     

A New Teletext Channel

A new method of transmitting data suitable for a teletext service is introduced. This is a channel that is time division multiplexed into the front porch Portion of the composite video and transmits two bits of information by virtue of a burst that can assume one of four possible phases, in the preferred form. It is intended to be used together with the conventional method of teletext transmission through the vertical blanking interval to substantially reduce the waiting time for page information acquisition and display. The system is shown to have an excellent resiliency to noise. It has good potential for cost effectiveness because it uses much of the circuitry already present in a color television for detection, synchronization, and processing.     

基于DVB机顶盒的VBI图文接收系统

介绍了DVB图文接收模式的硬件、软件设计及其实现，并在软件模式中提出了一种提高图文访问速度的方法，改善了图文接收系统的性能。     

Response Time in Data Broadcast Systems: Mean,Variance and Tradeoff

Data broadcast has been suggested as a promising method of information dissemination [2,33]. In such an environment, the information server cannot afford to serve the requests from a large population of users individually. Instead, the server uses a broadcast channel to deliver information to all users. A single transmission of a data item satisfies all pending requests for that item. The response time of a request depends on the broadcast time of the desired data item, which is scheduled by the server according to the overall demands for various data items. Therefore, the response time may vary in a large range. We argue that, in addition to mean response time, the variance of response time should also be taken into account by the broadcast scheduler. In this paper, we address the issue of variance optimization in regard to response time. Building on our previous research on mean response time optimization, we propose an algorithm which can minimize the variance of response time. Furthermore, we evaluate an algorithm that facilitates a tradeoff between the mean and variance of response time. Numerical examples that illustrate the performance of our algorithms are also presented.     

Use of blind equalization for teletext broadcast systems

A new application of blind equalization that appears to ameliorate the delays and improve the reliability of teletext systems is presented. The compatibility with the existing TV system and the cost-effectiveness of this application were considered for practical purposes. Equalizer adaptation does not require a knowledge of the transmitted data sequence or carrier phase recovery. Therefore, a reduction in the existing teletext circuitry has been achieved. In addition, the proposed quadrature phase shift keying (QPSK) modulation scheme doubles the teletext data transmission rate and uses the allocated TV bandwidth efficiently. The performance of the proposed blind equalizer has been evaluated in the presence of a multipath broadcast channel. Simulations have shown that substantial improvements are observed in the bit-error-rates for both two-phase PSK and QPSK modulation schemes     

CoopMAC: A Cooperative MAC for Wireless LANs

Due to the broadcast nature of wireless signals, a wireless transmission intended for a particular destination station can be overheard by other neighboring stations. A focus of recent research activities in cooperative communications is to achieve spatial diversity gains by requiring these neighboring stations to retransmit the overheard information to the final destination. In this paper we demonstrate that such cooperation among stations in a wireless LAN (WLAN) can achieve both higher throughput and lower interference. We present the design for a medium access control protocol called CoopMAC, in which high data rate stations assist low data rate stations in their transmission by forwarding their traffic. In our proposed protocol, using the overheard transmissions, each low data rate node maintains a table, called a CoopTable, of potential helper nodes that can assist in its transmissions. During transmission, each low data rate node selects either direct transmission or transmission through a helper node in order to minimize the total transmission time. Using analysis, simulation and testbed experimentation, we quantify the increase in the total network throughput, and the reduction in delay, if such cooperative transmissions are utilized. The CoopMAC protocol is simple and backward compatible with the legacy 802.11 system. In this paper, we also demonstrate a reduction in the signal-to-interference ratio in a dense deployment of 802.11 access points, which in some cases is a more important consequence of cooperation     

An error-correcting coding scheme for teletext and othertransparent data broadcasting

Nonprimitive and primitive Reed-Solomon (RS) codes (and product codes based on them) that can provide a very low bit error rate (BER) for the transparent data broadcasting feature of North American broadcast Teletext Specification (NABTS) are described. Transparent data consist of 8-b bytes, each without a parity-check bit, as contrasted with nontransparent data, which consist of 8 bit bytes, each of which has a parity-check bit in every byte. Specific applications for transparent error-coding codes constructed from RS codes in broadcast teletext broadcasting are discussed. Nonprimitive RS codes designed for nontransparent data broadcasting by NABTS teletext are derived, and powerful product forms of shortened nonprimitive Reed-Solomon codes are described     

Adaptive gossip protocols: Managing security and redundancy in dense ad hoc networks

Many ad hoc routing algorithms rely on broadcast flooding for location discovery or, more generally, for secure routing applications. Flooding is a robust algorithm but because of its extreme redundancy, it is impractical in dense networks. Indeed in large wireless networks, the use of flooding algorithms may lead to broadcast storms where the number of collisions is so large that it causes system failure. To prevent broadcast storms, many mechanisms that reduce redundant transmissions have been proposed that reduce retransmission overhead either deterministically or probabilistically.Gossip is a probabilistic algorithm in which packet retransmission is based on the outcome of coin tosses. The retransmission probability can be fixed, dynamic or adaptive. With dynamic gossip, local information is used to determine the retransmission probability. With adaptive gossip, the decision to relay is adjusted adaptively based on the outcome of coin tosses, the local network structure, and the local response to the flooding call. The goal of gossip is to minimize the number of retransmissions, while retaining the main benefits of flooding, e.g., universal coverage, minimal state retention, and path length preservation.In this paper we consider ways to reduce the number of redundant transmissions in flooding while guaranteeing security. We present several new gossip protocols that exploit local connectivity to adaptively correct propagation failures and protect against Byzantine attacks. A main contribution of this work is that we introduce a cell-grid approach that allows us to analytically prove performance and security protocol properties. The last two gossip protocols that we give are fully adaptive, i.e., they automatically correct all faults and guarantee delivery, the first such protocols to the best of our knowledge.     

Optimal Design of Broadcast Teletext Caption Preparation Systems

The provision of television captions for the benefit of the hearing impaired is the growing practice of many broadcasting organisations. This paper discusses the research and design work which led to the development of 'NEWFOR', a caption preparation system for broadcast teletext. Caption preparation is a complex and time-consuming task, which often required as long as 30-40 hours preparation time per captioned programme hour using early teletext origination systems. Research carried out into the display requirements for captioning for the hearing impaired led to a design specification for a stand alone caption preparation system and a handbook of guidelines on captioning. Analysis of the operational requirements of caption preparation provided a framework for optimal task division between the human captioner and the captioning computer. The system developed as a result halves caption preparation time, and also permits captioning of live programmes. The system described is now available commercially and is used for all teletext captioning by Independent Television in the UK.     

Modeling and performance of the North American Broadcast TeletextSystem with quasi-synchronous detection

In vestigial sideband systems the most critical region is the Nyquist region of the receiver response, which is difficult to control in practice, so that synchronous and quasi-synchronous detection are not perfect due to quadrature distortion. The advantages of phase-locked-loop quasi-synchronous detection and the factors influencing their design are discussed. These factors include incidental phase modulation introduced by the Nyquist slope of the receiver IF filter in response to synchronization signals, audio buzz, and the effects of other signal distortions. Analysis, modeling, and computer simulations have been used to study quasi-synchronous detection in Gaussian and impulse noise and multipath environments and to find carrier recovery phase error and teletext system performance curves. Possible improvements to television carrier recovery systems are suggested. It is concluded that well-designed quasi-synchronous carrier recovery loops suffer relatively minor degradations (about 0.5 dB) compared to narrowband (synchronous) carrier recovery, in multipath and noise environments of interest to broadcast teletext application     

Soft-decision decoding of the teletext character code

This letter proposes a soft-decision decoding algorithm as a means of improving the displayed-character error rate of teletext transmissions by simple modifications to the decoder only. The expected improvement is theoretically assessed, performance curves are given and implementation of the scheme is discussed.     

Response Time Analysis in a Data Broadcast System with User Cache

Data broadcast has been considered a promising way of information dissemination to a massive number of users in a wireless communication environment. Reducing user-waiting time is a major problem in developing a data broadcast system. There are two approaches for this problem; One is to design a broadcast schedule at the server side which reduces the mean response time, and the other is to utilize a local cache at the user side which may respond to a user request instantly. Though these two approaches were addressed separately in the literature, they may be taken jointly for better performance. The performance of system with joint approach depends on several factors such as broadcast schedule, cache size, cache management strategy, etc. In this paper we analyze response time in a data broadcast system with joint approach in which information items are structurally related with each other as in WWW. Based on the worst-case assumption, we derive a lower bound on the system performance for a given set of broadcast schedule, cache size, and cache management strategy. This result will be of help for designing and developing a data broadcast system. We support our analysis by carrying out an extensive simulation on some interesting proposed broadcast schedules and cache management strategies.