Stringent Delay Constraints Research Articles

Layered video multicast with a P2P cooperation approach

With the rapid development of wireless networking technology, real time video multicast applications have become feasible. These applications are bandwidth hungry and have stringent delay constraints. Furthermore, in wireless networks, different users generally have different receiving capabilities. Therefore, it is challenging to provide scalable support for such applications. To address this challenge, in this paper, we propose to use layered video and a P2P mode approach. In our solution, a video is encoded into multiple layers and broadcast to the multicast group users. Users form a P2P network to recover the loss of multicast video packets. This can significantly improve the overall received video quality. More importantly, our solution can provide incentives for users to help each other. With the proposed scheme, when a user helps another one, it can also improve its own received video quality.

On Queueing and Multilayer Coding

A single-server queue concatenated with a multilayer channel encoder is considered. The main focus of this work is on minimization of the expected delay of a packet from entering the queue until completion of successful service. Tight bounds are derived for the expected delay for different numbers of coded layers. Numerical optimization is applied to find the optimal resource allocation minimizing the average delay. Similar bounds are also derived for the case of continuous layering. It is demonstrated that code layering may give pronounced performance gains in terms of delay, which are more impressive than those associated with throughput. This makes layering more attractive when communicating under stringent delay constraints.

Optimized Bandwidth Utilization for Real Time Applications in Wireless Sensor Networks

Wireless sensor networks (WSNs) are special types of networks used in information gathering in military, industrial, and surveillance applications. Many such applications of WSNs require Quality of service (QoS) in terms of high bandwidth for real time applications including multimedia audio and video without much delay. These applications demand high packet delivery ratio and are extremely delay-sensitive. However, certain factors limit the ability of the multihop WSNs to achieve the desired goals. These factors include the delay caused by network congestion in the network, limited energy of the sensor nodes, packet loss due to collisions and link failure. In this paper, we propose an optimized bandwidth adaptation and utilization algorithm for real time applications in WSNs. The problem is formulated as linear programming (LP) together with specified constraints. Three types of applications (applications with strict delay requirements, applications with less stringent delay constraints and applications with delay tolerant capabilities) are considered for demonstration. Our claim is well supported with the simulation results carried on OMNET++ simulator.

Power allocation for two different traffics in layered MIMO systems

In multiple input multiple output (MIMO) relay networks, an MIMO node can relay different traffics from multiple MIMO source nodes. Thus, an MIMO relay node has to allocate the power across multiple channels to relay different traffics. In this paper, we consider the power allocation across multiple layers of MIMO channel when two different traffics, real-time and best-effort traffics, are presented. Generally, realtime traffics have stringent delay constraints and their data streams could not be multiplexed with the data streams from best-effort traffics due to different quality of service (QoS). Since MIMO channels can provide multiple parallel channels, we are able to transmit both different traffics separately (and simultaneously). For efficient power use, we investigate the power allocation across multiple parallel channels in presence of two different traffics with different performance index for each traffic. Performance analysis is carried out for uncorrelated Rayleigh-fading MIMO channels.

Call Admission Control and Scheduling Schemes with QoS Support for Real-time Video Applications in IEEE 802.16 Networks

IEEE 802.16 networks are going to provide broadband wireless access with quality of service (QoS) guarantee. In all of services, real-time video traffic plays an impeditive role because of its varying bit-rate and stringent delay constraint. To the best of our knowledge, no call admission control (CAC) and scheduling schemes cover throughput expectation, delay constraint and fairness requirement simultaneously. In this paper, by taking advantage of traffic periodicity and regularity, a set of CAC and scheduling schemes for real-time video traffic in IEEE 802.16 networks is proposed. Specifically, two key parameters are studied to compromise throughput and delay, as well as, delay and fairness. Simulations with real life video traces show that the proposed schemes may well bear flexibility in balancing throughput, delay and fairness, or, offering significant throughput improvement with acceptable delay and fairness.

Comparative rate-distortion performance of multiple description coding for real-time audiovisual communication over the Internet

To facilitate real-time audiovisual communication through the Internet, forward error correction (FEC) and multiple description coding (MDC) can be used as low-delay packet-loss recovery techniques. We use both a Gilbert channel model and data obtained from real IP connections to compare the rate-distortion performance of different variants of FEC and MDC. Using identical overall rates with stringent delay constraints, we find that side-distortion optimized MDC generally performs better than Reed-Solomon-based FEC. If the channel condition is known from feedback, then channel-optimized MDC can be used to exploit this information, resulting in significantly improved performance. Our results confirm that two-independent-channel transmission is preferred to single-channel transmission, both for FEC and MDC.

Optimized error protection of scalable image bit streams [advances in joint source-channel coding for images

This article focuses on FEC for scalable image coders. For various channel models, we survey recent progress made in system design and discuss efficient source-channel bit allocation techniques, with emphasis on unequal error protection. This article considered JSCC (joint source-channel coding) at the application layer only. Recent research has studied cross-layer optimization where JSCC is applied to both the application layer and the physical layer. The basic task here is to minimize the average distortion by allocating available power, subcarriers, and bandwidth among users at the physical layer and source-channel symbols at the application layer subject to a total resource constraint. Most of the JSCC systems covered in this article can be readily extended to transmit scalable compressed bit streams of video sequences and 3-D meshes. Due to the stringent delay constraints in video communications and the fact that MPEG is currently exploring a scalable video coding standard, fast JSCC algorithms are expected to play a bigger role and bring more performance gains. This article is also expected to stimulate further research efforts into JSCC and more importantly, prompt the industry to adopt some of these JSCC algorithms in their system designs, thus closing the cycle from algorithm development to implementation.

Transmitting to Colocated Users in Wireless Ad Hoc and Sensor Networks

We consider wireless ad hoc networks and sensor networks where a remotely located source is transmitting information to a destined user embedded within a group of K densely packed physically colocated users enjoying favorable signal-to-noise ratio (SNR) conditions among themselves, but suffering from quasi-static flat Rayleigh fading with respect to the source. Stringent delay constraints require that information, once available, be transmitted immediately and delivered reliably to its destination during a period of one fading block, precluding waiting until the destined user enjoys favorable fading conditions with respect to the source. A cooperative transmission strategy is proposed for this scenario and its expected throughput is investigated. The strategy exhibits a substantial gain in throughput, especially when the colocation gain factor is high. In addition, a broadcast approach is incorporated into the transmission strategy suggesting further throughput benefits.

Timing driven gate duplication

In the past few years, gate duplication has been studied as a strategy for cutset minimization in partitioning problems. This paper addresses the problem of delay optimization by gate duplication. We present an algorithm to solve the gate duplication problem. It traverses the network from primary outputs(PO) to primary inputs(PI) in topologically sorted order evaluating tuples at the input pins of gates. The tuple's first component corresponds to the input pin required time if that gate is not duplicated. The second component corresponds to the input pin required time if that gate were duplicated. After tuple evaluation the algorithm traverses the network from PI to PO in topologically sorted order, deciding the gates to be duplicated. The last and final traversal is again from PO to PI, in which the gates are physically duplicated. Our algorithm uses the dynamic programming structure. We report delay improvements over other optimization methodologies. Gate duplication, along with other optimization strategies, can be used for meeting the stringent delay constraints in today's ultra complex designs.