1,375 research outputs found
Improving packet delivery efficiency using multi-radio diversity in wireless LANs
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 115-120).Data transmissions in Wireless Local Area Networks (WLANs) often suffer from bit errors that arise from the notoriously complex and time-varying signal propagation characteristics of the wireless medium. A number of physical factors such as attenuation and multi-path are prevalent indoors and can lead to high bit-error rates at the link layer. These in turn lead to packet losses, low throughput, and higher and more variable packet latencies observed at higher layers, degrading the performance of many delay-sensitive and traffic-intensive wireless applications such as games, file-sharing, voice-over-IP, and streaming video. We use the notion of path diversity to develop an approach that improves data delivery efficiency and throughput in presence of transmission errors. Path diversity relies on multiple access points (APs) covering a given area or multiple radios on the user's device (or both). The hypothesis underlying this system is as follows: because frame errors are often path-dependent (e.g., due to multi-path fading), location-dependent (e.g., due to noise), and statistically independent between different transmitting radios, transmissions are likely to succeed from at least one of the available transmitters (transmit diversity).(cont.) Likewise, multiple radios that all receive versions of the same transmission may together be able to correctly recover a frame, even when any given individual radio is not (receive diversity). Using these principles, we design and implement the Multi-Radio Diversity (MRD) system, which leverages the properties of path diversity at the transmitter and receiver to reduce frame loss rates in the link-layer, leading to increased throughput and packet delivery efficiency. We introduce several techniques that make path selection, retransmission, and rate adaptation work efficiently in a MRD system based on the 802.11 MAC. We used commodity PCs and wireless interfaces to build a MRD system and conducted a wide range of indoor experiments. Our experiments measured throughput gains up to three times over conventional schemes without consuming much extra wireless bandwidth.by Allen Ka Lun Miu.Ph.D
Quantifying Potential Energy Efficiency Gain in Green Cellular Wireless Networks
Conventional cellular wireless networks were designed with the purpose of
providing high throughput for the user and high capacity for the service
provider, without any provisions of energy efficiency. As a result, these
networks have an enormous Carbon footprint. In this paper, we describe the
sources of the inefficiencies in such networks. First we present results of the
studies on how much Carbon footprint such networks generate. We also discuss
how much more mobile traffic is expected to increase so that this Carbon
footprint will even increase tremendously more. We then discuss specific
sources of inefficiency and potential sources of improvement at the physical
layer as well as at higher layers of the communication protocol hierarchy. In
particular, considering that most of the energy inefficiency in cellular
wireless networks is at the base stations, we discuss multi-tier networks and
point to the potential of exploiting mobility patterns in order to use base
station energy judiciously. We then investigate potential methods to reduce
this inefficiency and quantify their individual contributions. By a
consideration of the combination of all potential gains, we conclude that an
improvement in energy consumption in cellular wireless networks by two orders
of magnitude, or even more, is possible.Comment: arXiv admin note: text overlap with arXiv:1210.843
Game-theoretic Resource Allocation Methods for Device-to-Device (D2D) Communication
Device-to-device (D2D) communication underlaying cellular networks allows
mobile devices such as smartphones and tablets to use the licensed spectrum
allocated to cellular services for direct peer-to-peer transmission. D2D
communication can use either one-hop transmission (i.e., in D2D direct
communication) or multi-hop cluster-based transmission (i.e., in D2D local area
networks). The D2D devices can compete or cooperate with each other to reuse
the radio resources in D2D networks. Therefore, resource allocation and access
for D2D communication can be treated as games. The theories behind these games
provide a variety of mathematical tools to effectively model and analyze the
individual or group behaviors of D2D users. In addition, game models can
provide distributed solutions to the resource allocation problems for D2D
communication. The aim of this article is to demonstrate the applications of
game-theoretic models to study the radio resource allocation issues in D2D
communication. The article also outlines several key open research directions.Comment: Accepted. IEEE Wireless Comms Mag. 201
Multi-radio cooperative ARQ in wireless cellular networks: a MAC layer perspective
Multi-Radio Cooperative Automatic Retransmission Request (MCARQ)
schemes are introduced in this paper within the context of hybrid networks
which combine long-range and short-range communications. Since the number of
wireless devices is incessantly increasing, it is frequently possible to establish a
spontaneous cooperative cluster in the close proximity of any wireless device.
These devices forming the cluster are connected to both a cellular-based network
such as WiMAX, 3G, or LTE and a short-range network based on technologies
such as WLAN, Zigbee, Bluetooh, or UWB, among other possibilities. The main
idea behind the proposed MC-ARQ scheme is that, upon transmission error
through the cellular interface, retransmission can be requested to the wireless grid
surrounding the destination device using the short-range interface instead of the
primary cellular link. Therefore, besides the cooperative diversity attained with CARQ
schemes, the traffic load in the cellular interface is reduced benefiting thus a
high number of users and reducing both energy consumption and interference.
The Persistent Relay Carrier Sensing Medium Access (PRCSMA) protocol is
presented as an example of solution for the MAC layer in this emerging new topic.Postprint (published version
Spread spectrum techniques for indoor wireless IR communications
Multipath dispersion and fluorescent light
interference are two major problems in indoor
wireless infrared communications systems. Multipath
dispersion introduces intersymhol interference
at data rates above 10 Mb/s, while
fluorescent light induces severe narrowband
interference to baseband modulation schemes
commonly used such as OOK and PPM. This
article reviews the research into the application
of direct sequence spread spectrum techniques
to ameliorate these key channel impairments
without having to resort to complex signal processing
techniques. The inherent properties of a
spreading sequence are exploited in order to
combat the ISI and narrowband interference. In
addition, to reduce the impact of these impairments,
the DSSS modulation schemes have
strived to be bandwidth-efficient and simple to
implement. Three main DSSS waveform techniques
have been developed and investigated.
These are sequence inverse keying, complementary
sequence inverse keying, and M-ary biorthogonal
keying (MBOK). The operations of
the three systems are explained; their performances
were evaluated through simulations and
experiments for a number of system parameters,
including spreading sequence type and length.
By comparison with OOK, our results show that
SIK, CSIK, and MBOK are effective against
multipath dispersion and fluorescent light interference
becausc the penalties incurred on the
DSSS schemes are between 0-7 dB, while the
penalty on OOK in the same environment is
more than 17 dB. The DSSS solution for IR
wireless transmission demonstrates that a transmission
waveform can he designed to remove
the key channel impairments in a wireless IR
system
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