Jon M. Peha

Streaming video over the Internet: approaches and directions

Due to the explosive growth of the Internet and increasing demand for multimedia information on the Web, streaming video over the Internet has received tremendous attention from academia and industry. Transmission of real-time video typically has bandwidth, delay, and loss requirements. However, the current best-effort Internet does not offer any quality of service (QoS) guarantees to streaming video. Furthermore, for video multicast, it is difficult to achieve both efficiency and flexibility. Thus, Internet streaming video poses many challenges. In this article we cover six key areas of streaming video. Specifically, we cover video compression, application-layer QoS control, continuous media distribution services, streaming servers, media synchronization mechanisms, and protocols for streaming media. For each area, we address the particular issues and review major approaches and mechanisms. We also discuss the tradeoffs of the approaches and point out future research directions.

Sharing Spectrum Through Spectrum Policy Reform and Cognitive Radio

Traditionally, interference protection is guaranteed through a policy of spectrum licensing, whereby wireless systems get exclusive access to spectrum. This is an effective way to prevent interference, but it leads to highly inefficient use of spectrum. Cognitive radio along with software radio, spectrum sensors, mesh networks, and other emerging technologies can facilitate new forms of spectrum sharing that greatly improve spectral efficiency and alleviate scarcity, if policies are in place that support these forms of sharing. On the other hand, new technology that is inconsistent with spectrum policy will have little impact. This paper discusses policies that can enable or facilitate use of many spectrum-sharing arrangements, where the arrangements are categorized as being based on coexistence or cooperation and as sharing among equals or primary-secondary sharing. A shared spectrum band may be managed directly by the regulator, or this responsibility may be delegated in large part to a license-holder. The type of sharing arrangement and the entity that manages it have a great impact on which technical approaches are viable and effective. The most efficient and cost-effective form of spectrum sharing will depend on the type of systems involved, where systems under current consideration are as diverse as television broadcasters, cellular carriers, public safety systems, point-to-point links, and personal and local-area networks. In addition, while cognitive radio offers policy-makers the opportunity to improve spectral efficiency, cognitive radio also provides new challenges for policy enforcement. A responsible regulator will not allow a device into the marketplace that might harm other systems. Thus, designers must seek innovative ways to assure regulators that new devices will comply with policy requirements and will not cause harmful interference.

Spectrum management policy options

As market-based reform sweeps telecommunications industries around the world, it is a good time to reevaluate the spectrum management policies which govern wireless industries ranging from broadcast television to satellite communications. Most countries have been using a central planning approach to spectrum management, but there are many alternatives with varying degrees of flexibility and market-based incentives. This paper provides a survey of spectrum management approaches, addressing methods of determining how spectrum can be used, which commercial entities can use it, and how governments can manage their own spectrum. It identifies some of the crucial choices to be made, and summarizes advantages and disadvantages of each.

Regulatory and policy issues protecting public safety with better communications systems

The communications failure present in the September 11 World Trade Center tragedy served as the basis for this paper. These communications failures are not the result of simple operator error or a single design flaw. The problems are rooted in the basic technical architecture of the communications infrastructure used for public safety in the United States, and the policy that produced that infrastructure. This paper presents innovation in both technology and policy to address the many problems.

Wireless communications and coexistence for smart environments

Technology is emerging that will support the pervasive deployment of small intelligent devices that serve their owner and communicate using wireless transmissions. Collectively, these devices would provide a smart environment. Before this vision can become a reality, significant challenges must be overcome in the design of access protocols, and in spectrum management policies. Some devices in a smart environment must be able to communicate, and all devices in a smart environment must be able to coexist without excessive mutual interference. This article discusses various methods of achieving these goals, and the fundamental trade-offs involved. Some of the alternative methods include the allocation of unlicensed spectrum for this purpose, establishment of an etiquette that constrains access protocol designs, adoption of a full standard for access protocols, and the creation of a spectrum band manager.

Mobility patterns in microcellular wireless networks

This study investigates mobility patterns in microcellular wireless networks, based on measurements from the 802.11 based system that blankets the Carnegie Mellon University campus. We characterize the distribution of dwell time, which is the length of time that a mobile device remains in a cell until the next handoff, and sign-on interarrival time, which is the length of time between successive sign-ons from the same mobile device. Many researchers have assumed that these distributions are exponential, but our results based on empirical analysis show that dwell time and sign-on interarrival time can be accurately described using heavy-tailed arithmetic distributions that have infinite mean and variance. We also show that the number of handoffs per sign-on can be modeled accurately with a heavy-tailed distribution.

A narrowband approach to efficient PCS spectrum sharing through decentralized DCA access policies

This article addresses spectrum sharing and open access for personal communications services (PCS). Traditional regulation has allocated electromagnetic spectrum through fragmentation into mutually exclusive frequency blocks. Block allocation schemes produce trunking inefficiencies in the use of multiple narrowband RF channels. Broadband allocation schemes such as code division multiple access (CDMA) can accommodate multiple users on a single RF channel. Due to the near-far problem, the only way competing CDMA operators could share common spectrum is through collocation of cell sites, which hinders market mechanisms. An alternative approach is narrowband spectrum sharing through a decentralized dynamic channel assignment (DCA) approach, such as autonomous reuse partitioning (ARP). Multiple-operator DCA allocation schemes for low-tier PCS systems have been proposed in some countries. Under such an approach, competing operators use a common air interface to share the available spectrum. Open access can improve opportunities for competition in the provision of PCS. Other things being equal, a multi-operator DCA system outperforms that achievable by multiple carriers under a traditional fragmented spectrum, even for overlapping networks and unequal traffic loads. In this article we use a discrete event simulation to explore the spectrum efficiency implications of adopting a narrowband decentralized DCA/ARP spectrum-sharing policy. We explore as well regulatory measures so operators will deploy infrastructure instead of appropriating channels from competitors.

Spectrum sharing through dynamic channel assignment for open access to personal communications services

This paper focuses on a narrow band technical solution that uses decentralized spectrum sharing to facilitate open access among competing personal communications services (PCS) operators. Existing policies that apportion spectrum by fixed channel assignment (FCA) involve inefficiencies resulting from fragmentation of the available resource into mutually exclusive frequency blocks. Dynamic channel assignment (DCA) has been previously demonstrated to be flexible in handling traffic variability and to simplify frequency planning for a single network operator. We use a discrete event simulation to demonstrate that DCA with autonomous reuse partitioning (ARP) provides more capacity than standard DCA; this property still holds when channels are shared among multiple operators, with partially overlapping networks and unequal traffic shares. We explore the impact of limiting the maximum number of channels that can be assigned to one cell site as an incentive for operators to build more cells, rather than simply appropriating channels from competitors.

Evaluating scheduling algorithms for traffic with heterogeneous performance objectives

Two types of network traffic are considered: traffic with deadlines, for which the most important performance objective is based on loss rate and packets without deadlines, for which the most important performance objective is based on mean delay. An optional scheduling algorithm is presented to minimize weighted loss rate and weighted mean delay in the queues that form at the switches and at the network access points of a packet-switched network where weights reflect the relative importance of packets. The algorithm is intended as a standard for the comparison of the performance of other scheduling algorithms. The algorithm is more general and lower computational complexity than previously published algorithms, enabling performance evaluation of some important scenarios that could not previously have been considered. Using the optimal performance results of this algorithm, the performance of the first-come-first-served, static priority, and earliest deadline first scheduling algorithms is evaluated.<<ETX>>

Admission control algorithms for cellular systems

This paper evaluates call admission control algorithms for a cellular or microcellular system. Algorithms are evaluated based on two Quality of Service (QoS) metrics: the new call blocking probability, which is the probability that a new call is denied access to the system, and the forced-termination probability, which is the probability that a call that has been admitted will be terminated prior to the calls completion. Three novel algorithms are presented: the Weighted Sum Scheme, the Probability Index Scheme, and the Hybrid Control Scheme. The weighted sum scheme uses the weighted sum of the number of calls underway in various cells when making the admission decision. The probability index scheme computes a probability index, which reflects the forced-termination probability of a new call arrival, and admits those calls with low probability indexes. The hybrid control scheme combines these two approaches. These novel algorithms are compared with three known algorithms: the Reservation Scheme in which a specific number of channels are reserved in each cell for handoffs, the Linear Weighting Scheme in which the admission decision depends on the total number of calls underway in a group of cells, and the Distributed Admission Control Scheme in which the admission decision depends on the projected overload probabilities in the cell at which the new call arrives and adjacent cells. We show that the Hybrid Control Scheme yields the best performance, particularly during periods when load differs from the expected level. We also show that the simple Reservation Scheme performs remarkably well, often superior to more complex schemes that have been proposed.