91 research outputs found
On maximizing the throughput of opportunistic multicast in wireless cellular networks with erasure codes
In this paper, we discuss the opportunistic multicast scheduling (OMS) in a wireless network using erasure codes. Originally proposed for channels with erasures such as internet, erasure codes are found useful in wireless multicast to achieve better tradeoff between multiuser diversity and the multicast gain. In this work we investigated how to design an opportunistic multicast scheduling scheme which can efficiently improve the per user throughput capacity in a wireless network using erasure codes. Aiming at maximize the throughput, we proposed a maximal OMS (M-OMS) scheme which is inspired by the unicast maximal opportunistic scheduling. We build a system model and provide theoretical analysis on proposed M-OMS scheme. The proposed scheme shows substantial improvement over existing fixed selection ratio opportunistic multicast scheduling schemes (F-OMS). © 2011 IEEE.published_or_final_versionThe 2011 IEEE International Conference on Communications (ICC 2011), Kyoto, Japan, 5-9 June 2011. In Proceedings of the IEEE ICC, 2011, p. 1-
Coordinated Multicasting with Opportunistic User Selection in Multicell Wireless Systems
Physical layer multicasting with opportunistic user selection (OUS) is
examined for multicell multi-antenna wireless systems. By adopting a two-layer
encoding scheme, a rate-adaptive channel code is applied in each fading block
to enable successful decoding by a chosen subset of users (which varies over
different blocks) and an application layer erasure code is employed across
multiple blocks to ensure that every user is able to recover the message after
decoding successfully in a sufficient number of blocks. The transmit signal and
code-rate in each block determine opportunistically the subset of users that
are able to successfully decode and can be chosen to maximize the long-term
multicast efficiency. The employment of OUS not only helps avoid
rate-limitations caused by the user with the worst channel, but also helps
coordinate interference among different cells and multicast groups. In this
work, efficient algorithms are proposed for the design of the transmit
covariance matrices, the physical layer code-rates, and the target user subsets
in each block. In the single group scenario, the system parameters are
determined by maximizing the group-rate, defined as the physical layer
code-rate times the fraction of users that can successfully decode in each
block. In the multi-group scenario, the system parameters are determined by
considering a group-rate balancing optimization problem, which is solved by a
successive convex approximation (SCA) approach. To further reduce the feedback
overhead, we also consider the case where only part of the users feed back
their channel vectors in each block and propose a design based on the balancing
of the expected group-rates. In addition to SCA, a sample average approximation
technique is also introduced to handle the probabilistic terms arising in this
problem. The effectiveness of the proposed schemes is demonstrated by computer
simulations.Comment: Accepted by IEEE Transactions on Signal Processin
Whether and Where to Code in the Wireless Relay Channel
The throughput benefits of random linear network codes have been studied
extensively for wirelined and wireless erasure networks. It is often assumed
that all nodes within a network perform coding operations. In
energy-constrained systems, however, coding subgraphs should be chosen to
control the number of coding nodes while maintaining throughput. In this paper,
we explore the strategic use of network coding in the wireless packet erasure
relay channel according to both throughput and energy metrics. In the relay
channel, a single source communicates to a single sink through the aid of a
half-duplex relay. The fluid flow model is used to describe the case where both
the source and the relay are coding, and Markov chain models are proposed to
describe packet evolution if only the source or only the relay is coding. In
addition to transmission energy, we take into account coding and reception
energies. We show that coding at the relay alone while operating in a rateless
fashion is neither throughput nor energy efficient. Given a set of system
parameters, our analysis determines the optimal amount of time the relay should
participate in the transmission, and where coding should be performed.Comment: 11 pages, 12 figures, to be published in the IEEE JSAC Special Issue
on Theories and Methods for Advanced Wireless Relay
Instantly Decodable Network Coding: From Centralized to Device-to-Device Communications
From its introduction to its quindecennial, network coding has built a strong reputation for enhancing packet recovery and achieving maximum information flow in both wired and wireless networks. Traditional studies focused on optimizing the throughput of the system by proposing elaborate schemes able to reach the network capacity. With the shift toward distributed computing on mobile devices, performance and complexity become both critical factors that affect the efficiency of a coding strategy. Instantly decodable network coding presents itself as a new paradigm in network coding that trades off these two aspects. This paper review instantly decodable network coding schemes by identifying, categorizing, and evaluating various algorithms proposed in the literature. The first part of the manuscript investigates the conventional centralized systems, in which all decisions are carried out by a central unit, e.g., a base-station. In particular, two successful approaches known as the strict and generalized instantly decodable network are compared in terms of reliability, performance, complexity, and packet selection methodology. The second part considers the use of instantly decodable codes in a device-to-device communication network, in which devices speed up the recovery of the missing packets by exchanging network coded packets. Although the performance improvements are directly proportional to the computational complexity increases, numerous successful schemes from both the performance and complexity viewpoints are identified
Network coding meets multimedia: a review
While every network node only relays messages in a traditional communication system, the recent network coding (NC) paradigm proposes to implement simple in-network processing with packet combinations in the nodes. NC extends the concept of "encoding" a message beyond source coding (for compression) and channel coding (for protection against errors and losses). It has been shown to increase network throughput compared to traditional networks implementation, to reduce delay and to provide robustness to transmission errors and network dynamics. These features are so appealing for multimedia applications that they have spurred a large research effort towards the development of multimedia-specific NC techniques. This paper reviews the recent work in NC for multimedia applications and focuses on the techniques that fill the gap between NC theory and practical applications. It outlines the benefits of NC and presents the open challenges in this area. The paper initially focuses on multimedia-specific aspects of network coding, in particular delay, in-network error control, and mediaspecific error control. These aspects permit to handle varying network conditions as well as client heterogeneity, which are critical to the design and deployment of multimedia systems. After introducing these general concepts, the paper reviews in detail two applications that lend themselves naturally to NC via the cooperation and broadcast models, namely peer-to-peer multimedia streaming and wireless networkin
Algorithm design for scheduling and medium access control in heterogeneous mobile networks
Mención Internacional en el tÃtulo de doctorThe rapid growth of wireless mobile devices has led to saturation and congestion of wireless channels – a well-known fact. In the recent years, this issue is further exacerbated by the ever-increasing demand for traffic intensed multimedia content applications, which include but are not limited to social media, news and video streaming applications. Therefore the development of highly efficient content distribution technologies is of utmost importance, specifically to cope with the scarcity and the high cost of wireless resources. To this aim, this thesis investigates the challenges and the considerations required to design efficient techniques to improve the performance of wireless networks. Since wireless signals are prone to fluctuations and mobile users are, with high likelihood, have difference channel qualities, we particularly focus on the scenarios with heterogeneous user distribution. Further, this dissertation considers two main techniques to cope with mobile users demand and the limitation of wireless resources. Firstly, we propose an opportunistic multicast scheduling to efficiently distribute or disseminate data to all users with low delay. Secondly, we exploit the Millimeter-Wave (mm-Wave) frequency band that has a high potential of meeting the high bandwidth demand. In particular, we propose a channel access mechanism and a scheduling algorithm that take into account the limitation of the high frequency band (i.e., high path loss).
Multicast scheduling has emerged as one of the most promising techniques for multicast applications when multiple users require the same content from the base station. Unlike a unicast scheduler which sequentially serves the individual users, a multicast scheduler efficiently utilizes the wireless resources by simultaneously transmitting to multiple users. Precisely, it multiplies the gain in terms of the system throughput compared to unicast transmissions. In spite of the fact that multicast schedulers are more efficient than unicast schedulers, scheduling for multicast transmission is a challenging task. In particular, base station can only chose one rate to transmit to all users. While determining the rate for users with a similar instantaneous channel quality is straight forward, it is non-trivial when users have different instantaneous channel qualities, i.e., when the channel is heterogeneous. In such a scenario, on one hand, transmitting at a low rate results in low throughput. On the other hand, transmitting at a high rate causes some users to fail to receive the transmitted packet while others successfully receive it but with a rate lower than their maximum rate. The most common and simplest multicasting technique, i.e., broadcasting, transmits to all receivers using the maximum rate that is supported by the worst receiver.
In recent years, opportunistic schedulers have been considered for multicasting. Opportunistic multicast schedulers maximize instantaneous throughput and transmit at a higher rate to serve only a subset of the multicast users. While broadcasting suffers from high delay for all users due to low transmission rate, the latter causes a long delay for the users with worse channel quality as they always favor users with better channel quality. To address these problems, we designed an opportunistic multicast scheduling mechanism that aims to achieve high throughput as well as low delay. Precisely, we are solving the finite horizon problem for multicasting. Our goal is that all multicast users receive the same amount of data within the shortest amount of time.
Although our proposed opportunistic multicast scheduling mechanism improves the system throughput and reduces delay, a common problem in multicast scheduling is that its throughput performance is limited by the worst user in the system. To overcome this problem, transmit beamforming can be used to adjust antenna gains to the different receivers. This allows improving the SNR of the receiver with the worst channel SNR at the expense of worsening the SNR of the better channel receivers. In the first part of this thesis, two different versions of the finite horizon problem are considered: (i) opportunistic multicast scheduling and (ii) opportunistic multicast beamforming.
In recent years, many researchers venture into the potential of communication over mm-Wave band as it potentially solves the existing network capacity problem. Since beamforming is capable to concentrate the transmit energy in the direction of interest, this technique is particularly beneficial to improve signal quality of the highly attenuated mm-Wave signal. Although directional beamforming in mm-Wave offers multi-gigabit-per-second data rates, directional communication severely deteriorates the channel sensing capability of a user. For instance, when a user is not within the transmission coverage or range of the communicating users, it is unable to identify the state of the channel (i.e., busy or free). As a result, this leads to a problem commonly known as the deafness problem. This calls for rethinking of the legacy medium access control and scheduling mechanisms for mm-Wave communication. Further, without omni-directional transmission, disseminating or broadcasting global information also becomes complex. To cope with these issues, we propose two techniques in the second part of this thesis. First, leveraging that recent mobile devices have multiple wireless interface, we present a dual-band solution. This solution exploits the omni-directional capable lower frequency bands (i.e., 2.4 and 5 GHz) to transmit control messages and the mm-Wave band for high speed data transmission. Second, we develop a decentralized scheduling technique which copes with the deafness problem in mm-Wave through a learning mechanism.
In a nutshell, this thesis explores solutions which (i) improve the utilization of the network resources through multicasting and (ii) meet the mobile user demand with the abundant channel resources available at high frequency bands.This work has been supported by IMDEA Networks Institute.Programa Oficial de Doctorado en IngenierÃa TelemáticaPresidente: Ralf Steinmetz.- Secretario: Carlos Jesús Bernardos Cano.- Vocal: Jordi Domingo Pascua
Random Linear Network Coding for Wireless Layered Video Broadcast: General Design Methods for Adaptive Feedback-free Transmission
This paper studies the problem of broadcasting layered video streams over
heterogeneous single-hop wireless networks using feedback-free random linear
network coding (RLNC). We combine RLNC with unequal error protection (UEP) and
our main purpose is twofold. First, to systematically investigate the benefits
of UEP+RLNC layered approach in servicing users with different reception
capabilities. Second, to study the effect of not using feedback, by comparing
feedback-free schemes with idealistic full-feedback schemes. To these ends, we
study `expected percentage of decoded frames' as a key content-independent
performance metric and propose a general framework for calculation of this
metric, which can highlight the effect of key system, video and channel
parameters. We study the effect of number of layers and propose a scheme that
selects the optimum number of layers adaptively to achieve the highest
performance. Assessing the proposed schemes with real H.264 test streams, the
trade-offs among the users' performances are discussed and the gain of adaptive
selection of number of layers to improve the trade-offs is shown. Furthermore,
it is observed that the performance gap between the proposed feedback-free
scheme and the idealistic scheme is very small and the adaptive selection of
number of video layers further closes the gap.Comment: 15 pages, 12 figures, 3 tables, Under 2nd round of review, IEEE
Transactions on Communication
WIMAX Basics from PHY Layer to Scheduling and Multicasting Approaches
WiMAX (Worldwide Interoperability for Microwave Access) is an emerging broadband wireless technology for providing Last mile solutions for supporting higher bandwidth and multiple service classes with various quality of service requirement. The unique architecture of the WiMAX MAC and PHY layers that uses OFDMA to allocate multiple channels with different modulation schema and multiple time slots for each channel allows better adaptation of heterogeneous user’s requirements. The main architecture in WiMAX uses PMP (Point to Multipoint), Mesh mode or the new MMR (Mobile Multi hop Mode) deployments where scheduling and multicasting have different approaches. In PMP SS (Subscriber Station) connects directly to BS (Base Station) in a single hop route so channel conditions adaptations and supporting QoS for classes of services is the key points in scheduling, admission control or multicasting, while in Mesh networks SS connects to other SS Stations or to the BS in a multi hop routes, the MMR mode extends the PMP mode in which the SS connects to either a relay station (RS) or to Bs. Both MMR and Mesh uses centralized or distributed scheduling with multicasting schemas based on scheduling trees for routing. In this paper a broad study is conducted About WiMAX technology PMP and Mesh deployments from main physical layers features with differentiation of MAC layer features to scheduling and multicasting approaches in both modes of operations
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