Single Broadcast Channel Research Articles

A Lower Bound for Adaptively-Secure Collective Coin Flipping Protocols

In 1985, Ben-Or and Linial (Advances in Computing Research 1989) introduced the collective coin flipping problem, where n parties communicate via a single broadcast channel and wish to generate a common random bit in the presence of adaptive Byzantine corruptions. In this model, the adversary can decide to corrupt a party in the course of the protocol as a function of the messages seen so far. They showed that the majority protocol, in which each player sends a random bit and the output is the majority value, tolerates O(√n) adaptive corruptions. They conjectured that this is optimal for such adversaries. We prove that the majority protocol is optimal (up to a poly-logarithmic factor) among all protocols in which each party sends a single, possibly long, message. Previously, such a lower bound was known for protocols in which parties are allowed to send only a single bit (Lichtenstein, Linial, and Saks, Combinatorica 1989), or for symmetric protocols (Goldwasser, Kalai, and Park, ICALP 2015).

Channel Correlation Based Zero-Forcing Beamforming in Two-User MISO Broadcast Channel

In this paper, a novel zero-forcing beamforming (ZFBF) is presented for the two-user multiple input single output broadcast channel. Based on the knowledge of channel correlations at the transmitter side, a nonlinear optimization problem is formulated to determine the beamformers so that the weighted ergodic sum-rate is maximized subject to avoiding multi-user interference and meeting a total power constraint. By factorizing each beamformer, the original complicated problem can be transformed into a simpler one. Numerical results show that the performance gap between the proposed ZFBF and the traditional instantaneous channel state information based ZFBF is within 1.5 bits per transmission.

Channel dynamic adjustment in data broadcast

Data broadcasting has become the preferred method to dispense data to a large number of mobile users. Current researches on on-demand data broadcast mainly propose algorithms based on a single broadcast channel or fixed multi-channel, i.e., fixed channel model. As a result of the dynamic diversity of data characteristics and client demands, the fixed channel model faces significant challenges in parallel broadcast diverse data. Further, the dynamic adjustment of the broadcast channel (dynamic channel model) based on client requests is favorable to service quality because it determines the number and sizes of channels that adapt to client demand in real-time. However, the dynamic channel model has not yet been thoroughly investigated for on-demand wireless data broadcasts. Accordingly, in this paper, a channel dynamic adjustment method (CDAM) is proposed. The innovations behind CDAM lie in three aspects. First, a data item priority evaluation and selection algorithm (S-RxW/SL) is proposed for evaluating the priority of data items and selecting the high priority data items to be considered in a broadcast cycle. Second, a weight and size average cluster algorithm (WSAC) is proposed for mining data item characteristics and clustering them. Third, based on the clustering results of WSAC, a channel splitting and data allocation algorithm (CSDA) is proposed for dynamically splitting the channel and allocating data items to the corresponding sub-channel. We compare the proposed method with some state-of-the-art scheduling methods through simulation. The theoretical findings and simulation results reveal that significantly better request loss rate (LR) can be obtained by using our method as compared to its alternatives.

A Spatial Indexing Scheme for Location Based Service Queries in a Single Wireless Broadcast Channel

The rapid advancement of mobile devices and wireless network technology has accelerated the development of applications in the mobile computing field. In particular, LBS (Location-Based Services) are one of the fastest growing areas in mobile applications. In a wireless data broadcasting environment, a server can effectively provide LBS to a large population of mobile clients. The two most typical types of LBS queries are window and kNN (k-Nearest Neighbors) queries. Previously proposed window and kNN query processing schemes in a single wireless broadcast channel environment tend to access much unnecessary index information and data objects due to their low filtering powers. In this paper, we propose a new spatial index called HMI (Hilbert curve-based MBR filtering Index) for the efficient processing of window and kNN queries in a single wireless broadcast channel. HMI is a tree-structured index whose construction is based on the Hilbert curve and MBR (Minimum Bounding Rectangle). By combining an MBR structure with the Hilbert curve order, HMI obtains the advantages of both structures. We present an in-depth experimental analysis of our method by comparing it with current existing schemes. Our performance analysis shows that HMI significantly decreases the average access and tuning times of kNN queries over current existing schemes. HMI also gives better average tuning times and comparable average access times of window queries over current existing schemes.

Multi-channel Broadcast via Channel Hopping in Cognitive Radio Networks

Broadcast is a mandatory service for wireless communications, through which the signals or contents are usually propagated as broadcasts to groups of users that subscribe to the service. However, in cognitive radio networks where secondary users (SUs) opportunistically access the licensed spectrum bands, the broadcast delivery via a single broadcast channel cannot be reliably guaranteed when the broadcast channel is reclaimed by a primary user (PU, or licensed user) that has a higher priority of accessing the spectrum or when an SU moves into a region where PU transmissions are active. As a result, broadcast failures occur between the base station (BS) and the SU. To address this problem, the BS has to broadcast on more than one channel to avoid colliding with PUs and ensure that all users can correctly receive the broadcasted content. In this paper, we propose a multichannel broadcast protocol, i.e., Mc-Broadcast, that enables a network BS to broadcast over multiple channels via a channel hopping (CH) process such that the broadcasts can be successfully delivered to SUs. The CH sequence for Mc-Broadcast is generated using a mathematical construct called Langford pairing, which allows the BS to significantly reduce the broadcast latency and given a customized number of broadcast channels. Our analytical and simulation results show that the proposed method reduces the broadcast latency, and it is robust to the broadcast failure caused by PU transmissions under various network conditions.

Broadcasting on-demand data with time constraints using multiple channels in wireless broadcast environments

Data Broadcasting is an effective approach to provide information to a large group of clients in ubiquitous environments. How to generate the data broadcast schedule to make the clients’ average waiting time as short as possible is an important issue. In particular, when the data access pattern is dynamic and data have time constraints, such as traffic and stock information, scheduling the broadcast for such data to fulfill the requests is challenging. Since the content of the broadcast is dynamic and the request deadlines should be met, such data broadcasting is referred to as on-demand data broadcasting with time constraints. Many papers have discussed this type of data broadcasting with a single broadcast channel. In this paper, we investigate how to schedule the on-demand broadcast for the data with time constraints using multiple broadcast channels and provide two heuristics to schedule the data broadcast. The objective of the proposed heuristics is to minimize the miss rate (i.e., ratio of the number of requests missing deadlines to the number of all requests) and latency (i.e., time between issuing and termination of the request). We show that the offline version of the considered problem is NP-hard and present a competitive analysis on the proposed heuristics. More discussion about the proposed heuristics is given through extensive simulation experiments. The experimental results validate that the proposed heuristics achieve the objectives.

A dynamic programming approach of finding an optimal broadcast schedule in minimizing total flow time

We study the problem of (off-line) broadcast scheduling in minimizing total flow time and propose a dynamic programming approach to compute an optimal broadcast schedule. Suppose the broadcast server has k pages and the last page request arrives at time n. The optimal schedule can be computed in O(k3(n+k)k−1) time for the case that the server has a single broadcast channel. For m channels case, i.e., the server can broadcast m different pages at a time where m < k, the optimal schedule can be computed in O(nk−m) time when k and m are constants. Note that this broadcast scheduling problem is NP-hard when k is a variable and will take O(nk−m+1) time when k is fixed and m ≥ 1 with the straightforward implementation of the dynamic programming approach.

Adaptive Multichannel Data Dissemination: Support of Dynamic Traffic Awareness and Push–Pull Time Balance

Data dissemination by the use of periodic broadcast is a viable scalable mechanism due to the explosion of information services in wireless networks. Many research works have exploited the data broadcast methodologies, however, upon the premise that the broadcast traffic is static on a single broadcast channel. In practice, the broadcast traffic changes dynamically and multiple broadcast channels can be utilized for efficient data dissemination. Accordingly, in this paper we devise an adaptive multichannel data-dissemination mechanism, including two components: the multichannel traffic-awareness and the deterministic balance search techniques. The multichannel traffic-awareness technique performs a cyclic estimation of dynamic access frequency distribution in response to traffic dynamics. With the measured estimation, the deterministic balance search technique adjusts channel allocation and item classification to further minimize and balance the push access and the pull response time. The experimental results show that the proposed mechanism is able to attain the result of channel partition and item classification very close to the optimum and, thus, minimize the mean access time in both push and pull channels simultaneously. Therefore, the reliability of broadcast contents is guaranteed.

Dependent data broadcasting for unordered queries in a multiple channel mobile environment

Data broadcast is a promising technique to improve the bandwidth utilization and conserve the power consumption in a mobile computing environment. In many applications, the data items broadcast are dependent upon one another. However, most prior studies on broadcasting dependent data are restricted to a single broadcast channel environment, and as a consequence, the results are of limited applicability to the upcoming mobile environments. In view of this, we relax this restriction and explore the problem of broadcasting dependent data in multiple broadcast channels. By analyzing the model of dependent data broadcasting, we derive several theoretical properties for the average access time in a multiple channel environment. In light of the theoretical results, we develop a genetic algorithm to generate broadcast programs. Our experimental results show that the theoretical results derived are able to guide the search of the genetic algorithm very effectively, thus leading to broadcast programs of very high quality.

Nearly optimal perfectly periodic schedules

We consider the problem of scheduling a set of pages on a single broadcast channel using time-multiplexing. In a perfectly periodic schedule, time is divided into equal size slots, and each page is transmitted in a time slot precisely every fixed interval of time (the period of the page). We study the case in which each page i has a given demand probability wi, and the goal is to design a perfectly periodic schedule that minimizes the average time a random client waits until its page is transmitted. We seek approximate polynomial solutions. Approximation bounds are obtained by comparing the costs of a solution provided by an algorithm and a solution to a relaxed (non-integral) version of the problem. A key quantity in our methodology is a fraction we denote by a1, that depends on the maximum demand probability: a1 =def√maxi {wi}/Σ√wi. The best known polynomial algorithm to date guarantees an approximation of 3/2 + 3/2 a1. In this paper, we develop a tree-based methodology for perfectly periodic scheduling, and using new techniques, we derive algorithms with better bounds. For small a1 values, our best algorithm guarantees approximation of 1 + 3√3a1/1-3√3a1. On the other hand, we show that the integrality gap between the cost of any perfectly periodic schedule and the cost of the fractional problem is at least 1 + a12. We also provide algorithms with good performance guarantees for large values of a1.

Object Organization on a Single Broadcast Channel in the Mobile Computing Environment

Advances in computation and communication technologies allow users to access computer networks, using portable computing devices via a wireless connection, while mobile. Furthermore, multidatabases offer practical means of managing information sharing from multiple preexisting heterogeneous databases. By superimposing the mobile computing environment onto the multidatabase system, a new computing environment is attained. In this work, we concentrate on the effects of the mobile-computing environment on query processing in multidatabases. We show how broadcasting, as a possible solution, would respond to current challenges such as bandwidth and storage limitations. Organizing data objects along a single-dimension broadcast channel should follow the semantic links assumed within the multiple-dimension objects‘ structure. Learning from our past experiences in objects organization on conventional storage mediums (disks), we propose schemes for organizing objects along a single broadcast air channel. The proposed schemes are simulated and analyzed.

The effects of destructive interference and wasted transmissions on the uniform-traffic capacity of non-bus-oriented single-hop interconnections

The most prominent single-hop interconnection (SHI) topology is the single broadcast channel, or bus, which is used in local area networks (LANs) such as Ethernet. The uniform-traffic capacity of switchless, non-bus-oriented, fiber-optic SHIs among N stations, each equipped with a small number of transmitters and receivers, can be as high as /spl Theta/(log/sub 2/N) concurrent transmissions on a single wavelength with round-robin scheduling in a time-slotted system. However, their capacity with the slotted ALOHA access scheme does not increase with N. (The capacity of bus-oriented interconnections, in contrast, varies across time-slotted access schemes by, at most, a factor of e.) This paper quantifies the contribution of several factors to capacity. Merely avoiding destructive interference with ongoing receptions contributes, at most, a factor of e over slotted ALOHA, the same as in bus-oriented interconnections. For an interconnection among two-transmitter, single-receiver stations, whose capacity is log/sub 2/N with global scheduling and 2/e with slotted ALOHA, also avoiding transmissions to blocked receivers increases capacity to, at most, log/sub 2/log/sub 2/N. These results suggest that the added complexity of non-bus-oriented SHIs may be warranted only if they are operated in ways that permit the selection of good combinations of (source, destination) pairs for concurrent transmission, and further research should focus on those.

Broadcast disks

This paper proposes the use of repetitive broadcast as a way of augmenting the memory hierarchy of clients in an asymmetric communication environment. We describe a new technique called "Broadcast Disks" for structuring the broadcast in a way that provides improved performance for non-uniformly accessed data. The Broadcast Disk superimposes multiple disks spinning at different speeds on a single broadcast channel--in effect creating an arbitrarily fine-grained memory hierarchy. In addition to proposing and defining the mechanism, a main result of this work is that exploiting the potential of the broadcast structure requires a re-evaluation of basic cache management policies. We examine several "pure" cache management policies and develop and measure implementable approximations to these policies. These results and others are presented in a set of simulation studies that substantiates the basic idea and develops some of the intuitions required to design a particular broadcast program.

Universally attainable error exponents for broadcast channels with degraded message sets

Universally attainable error exponents for broadcast channels with degraded message sets are obtained using a technique which generalizes that introduced by Csiszar, Korner, and Martron for the ordinary channel. Lower and upper bounds to the error probabilities over a single broadcast channel are also given.

ALOHA packet system with and without slots and capture

This paper was originally distributed informally as ARPA Satellite System Note 8 on June 26, 1972. The paper is an important one and since its initial limited distribution, the paper has been frequently referenced in the open literature, but the paper itself has been unavailable in the open literature. Publication here is meant to correct the previous gap in the literature. As the paper was originally distributed only to other researchers intimately familiar with the area covered by the paper, the paper makes few concessions to the reader along the lines of introductory or tutorial material. Therefore, a bit of background material follows. ALOHA packet systems were originally described by Abramson ("The ALOHA System--Another Alternative for Computer Communication," Proceedings of the AFIPS Fall Joint Computer Conference, Vol. 37, 1970, pp. 281--285). In an ALOHA a single broadcast channel is shared by a number of communicating devices. In the version originally described by Abramson, every device transmits its packets independent of any other device or any specific time. That is, the device transmits the whole packet at a random point in time; the device then times out for receiving an acknowledgment. If an acknowledgment is not received, it is assumed that a collision occured with a packet transmitted by some other device and the packet is retransmitted after a random additional waiting time (to avoid repeated collisions). Under a certain set of assumptions, Abramson showed that the effective capacity of such a channel is 1/(2e). Roberts in the present paper investigates methods of increasing the effective channel capacity of such a channel. One method he proposes to gain in capacity is to consider the channel to be slotted into segments of time whose duration is equal to the packet transmission time, and to require the devices to begin a packet transmission at the beginning of a time slot. Another method Roberts proposes to gain in capacity is to take advantage of the fact that even though packets from two devices collide in the channel (i.e., they are transmitted so they pass through the channel at overlapping times), it may be possible for the receiver(s) to "capture" the signal of one of the transmitters, and thus correctly receive one of the conflicting packets, if one of the transmitters has a sufficiently greater signal than the other. Roberts considers the cases of both satellite and ground radio channels.