281 research outputs found
Towards a System Theoretic Approach to Wireless Network Capacity in Finite Time and Space
In asymptotic regimes, both in time and space (network size), the derivation
of network capacity results is grossly simplified by brushing aside queueing
behavior in non-Jackson networks. This simplifying double-limit model, however,
lends itself to conservative numerical results in finite regimes. To properly
account for queueing behavior beyond a simple calculus based on average rates,
we advocate a system theoretic methodology for the capacity problem in finite
time and space regimes. This methodology also accounts for spatial correlations
arising in networks with CSMA/CA scheduling and it delivers rigorous
closed-form capacity results in terms of probability distributions. Unlike
numerous existing asymptotic results, subject to anecdotal practical concerns,
our transient one can be used in practical settings: for example, to compute
the time scales at which multi-hop routing is more advantageous than single-hop
routing
A Network Calculus Approach for the Analysis of Multi-Hop Fading Channels
A fundamental problem in the delay and backlog analysis across multi-hop
paths in wireless networks is how to account for the random properties of the
wireless channel. Since the usual statistical models for radio signals in a
propagation environment do not lend themselves easily to a description of the
available service rate on a wireless link, the performance analysis of wireless
networks has resorted to higher-layer abstractions, e.g., using Markov chain
models. In this work, we propose a network calculus that can incorporate common
statistical models of fading channels and obtain statistical bounds on delay
and backlog across multiple nodes. We conduct the analysis in a transfer
domain, which we refer to as the `SNR domain', where the service process at a
link is characterized by the instantaneous signal-to-noise ratio at the
receiver. We discover that, in the transfer domain, the network model is
governed by a dioid algebra, which we refer to as (min,x)-algebra. Using this
algebra we derive the desired delay and backlog bounds. An application of the
analysis is demonstrated for a simple multi-hop network with Rayleigh fading
channels and for a network with cross traffic.Comment: 26 page
Energy-efficient diversity combining for different access schemes in a multi-path dispersive channel
Dissertação para obtenção do Grau de Doutor em
Engenharia Electrotécnica e ComputadoresThe forthcoming generation of mobile communications, 5G, will settle a new standard for a larger bandwidth and better Quality of Service (QoS). With the exploding growth rate of user generated data, wireless
standards must cope with this growth and at the same time be energy efficient to avoid depleting the batteries of wireless devices. Besides these issues, in a broadband wireless setting QoS can be severely affected from a multipath dispersive channel and therefore be energy demanding.
Cross-layered architectures are a good choice to enhance the overall performance of a wireless system.
Examples of cross-layered Physical (PHY) - Medium Access Control (MAC) architectures are type-II Diversity Combining (DC) Hybrid-ARQ (H-ARQ) and Multi-user Detection (MUD) schemes. Cross-layered type-II DC H-ARQ schemes reuse failed packet transmissions to enhance data reception on posterior retransmissions; MUD schemes reuse data information from previously collided packets on posterior retransmissions to enhance data reception. For a multipath dispersive channel, a PHY layer analytical
model is proposed for Single-Carrier with Frequency Domain Equalization (SC-FDE) that supports DC H-ARQ and MUD. Based on this analytical model, three PHY-MAC protocols are proposed. A crosslayered Time Division Multiple Access (TDMA) scheme that uses DC H-ARQ is modeled and its performance is studied in this document; the performance analysis shows that the scheme performs better with DC and achieves a better energy efficiency at the cost of a higher delay. A novel cross-layered prefix-assisted Direct-Sequence Code Division Multiple Access (DS-CDMA) scheme is proposed and modeled in this document, it uses principles of DC and MUD. This protocol performs better by means
of additional retransmissions, achieving better energy efficiency, at the cost of higher redundancy from a code spreading gain. Finally, a novel cross-layered protocol H-ARQ Network Division Multiple Access (H-NDMA) is proposed and modeled, where the combination of DC H-ARQ and MUD is used with the intent of maximizing the system capacity with a lower delay; system results show that the proposed scheme achieves better energy efficiency and a better performance at the cost of a higher number of retransmissions.
A comparison of the three cross-layered protocols is made, using the PHY analytical model, under normalized conditions using the same amount of maximum redundancy. Results show that the H-NDMA protocol, in general, obtains the best results, achieving a good performance and a good energy efficiency
for a high channel load and low Signal-to-Noise Ratio (SNR). TDMA with DC H-ARQ achieves the best energy efficiency, although presenting the worst delay. Prefix-assisted DS-CDMA in the other hand shows good delay results but presents the worst throughput and energy efficiency
Low-latency Networking: Where Latency Lurks and How to Tame It
While the current generation of mobile and fixed communication networks has
been standardized for mobile broadband services, the next generation is driven
by the vision of the Internet of Things and mission critical communication
services requiring latency in the order of milliseconds or sub-milliseconds.
However, these new stringent requirements have a large technical impact on the
design of all layers of the communication protocol stack. The cross layer
interactions are complex due to the multiple design principles and technologies
that contribute to the layers' design and fundamental performance limitations.
We will be able to develop low-latency networks only if we address the problem
of these complex interactions from the new point of view of sub-milliseconds
latency. In this article, we propose a holistic analysis and classification of
the main design principles and enabling technologies that will make it possible
to deploy low-latency wireless communication networks. We argue that these
design principles and enabling technologies must be carefully orchestrated to
meet the stringent requirements and to manage the inherent trade-offs between
low latency and traditional performance metrics. We also review currently
ongoing standardization activities in prominent standards associations, and
discuss open problems for future research
Scheduling in CDMA-based wireless packet networks.
Thesis (M.Sc. Eng.)-University of Natal, Durban, 2003.Modern networks carry a wide range of different data types, each with its own individual
requirements. The scheduler plays an important role in enabling a network to meet all
these requirements. In wired networks a large amount of research has been performed
on various schedulers, most of which belong to the family of General Processor Sharing
(GPS) schedulers. In this dissertation we briefly discuss the work that has been done on a
range of wired schedulers, which all attempt to differentiate between heterogeneous traffic.
In the world of wireless communications the scheduler plays a very important role, since
it can take channel conditions into account to further improve the performance of the
network. The main focus of this dissertation is to introduce schedulers, which attempt to
meet the Quality of Service requirements of various data types in a wireless environment.
Examples of schedulers that take channel conditions into account are the Modified Largest
Weighted Delay First (M-LWDF), as well as a new scheduler introduced in this dissertation,
known as the Wireless Fair Largest Weighted Delay First (WF-LWDF) algorithm.
The two schemes are studied in detail and a comparison of their throughput, delay, power,
and packet dropping performance is made through a range of simulations. The results are
compared to the performance offour other schedulers. The fairness ofM-LWDF and WFLWDF
is determined through simulations. The throughput results are used to establish
Chernoff bounds of the fairness of these two algorithms. Finally, a summary is given of the
published delay bounds of various schedulers, and the tightness of the resultant bounds is
discussed
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