44 research outputs found
Network-Coded Multiple Access
This paper proposes and experimentally demonstrates a first wireless local
area network (WLAN) system that jointly exploits physical-layer network coding
(PNC) and multiuser decoding (MUD) to boost system throughput. We refer to this
multiple access mode as Network-Coded Multiple Access (NCMA). Prior studies on
PNC mostly focused on relay networks. NCMA is the first realized multiple
access scheme that establishes the usefulness of PNC in a non-relay setting.
NCMA allows multiple nodes to transmit simultaneously to the access point (AP)
to boost throughput. In the non-relay setting, when two nodes A and B transmit
to the AP simultaneously, the AP aims to obtain both packet A and packet B
rather than their network-coded packet. An interesting question is whether
network coding, specifically PNC which extracts packet (A XOR B), can still be
useful in such a setting. We provide an affirmative answer to this question
with a novel two-layer decoding approach amenable to real-time implementation.
Our USRP prototype indicates that NCMA can boost throughput by 100% in the
medium-high SNR regime (>=10dB). We believe further throughput enhancement is
possible by allowing more than two users to transmit together
Servicing Delay Sensitive Pervasive Communication Through Adaptable Width Channelization for Supporting Mobile Edge Computing
Over the last fifteen years, wireless local area
networks (WLANs) have been populated by large variety of pervasive devices hosting heterogeneous applications. Pervasive Edge computing encouraged more distributed network applications for these devices, eliminating the round-trip to help in achieving zero latency dream. However, These applications require significantly variable data rates for effective functioning, especially in pervasive computing. The static bandwidth of frequency channelization in current WLANs strictly restricts
the maximum achievable data rate by a network station. This static behavior spawns two major drawbacks: under-utilization of scarce spectrum resources and less support to delay sensitive applications such as voice and video.To this point, if the computing is moved to the edge of the network WLANs to reduce the frequency of communication, the pervasive devices can be provided with better services during the communication and networking. Thus, we aim to distribute spectrum resources among pervasive resources based upon delay sensitivity of
applications while simultaneously maintaining the fair channel access semantics of medium access control (MAC) layer of WLANs. Henceforth, ultra-low latency, efficiency and reliability of spectrum resources can be assured. In this paper, two novel algorithms have been proposed
for adaptive channelization to offer rational distribution of spectrum resources among pervasive Edge nodes based on their bandwidth requirement and assorted ambient conditions. The proposed algorithms have been implemented on a real test bed of commercially available universal software radio peripheral (USRP) devices. Thorough investigations have been carried out to enumerate the effect of dynamic bandwidth channelization on parameters such as medium utilization,
achievable throughput, service delay, channel access fairness
and bit error rates. The achieved empirical results demonstrate that we can optimally enhance the network-wide throughput by almost 30% using channels of adaptable bandwidths
Sub-Nanosecond Time of Flight on Commercial Wi-Fi Cards
Time-of-flight, i.e., the time incurred by a signal to travel from
transmitter to receiver, is perhaps the most intuitive way to measure distances
using wireless signals. It is used in major positioning systems such as GPS,
RADAR, and SONAR. However, attempts at using time-of-flight for indoor
localization have failed to deliver acceptable accuracy due to fundamental
limitations in measuring time on Wi-Fi and other RF consumer technologies.
While the research community has developed alternatives for RF-based indoor
localization that do not require time-of-flight, those approaches have their
own limitations that hamper their use in practice. In particular, many existing
approaches need receivers with large antenna arrays while commercial Wi-Fi
nodes have two or three antennas. Other systems require fingerprinting the
environment to create signal maps. More fundamentally, none of these methods
support indoor positioning between a pair of Wi-Fi devices
without~third~party~support.
In this paper, we present a set of algorithms that measure the time-of-flight
to sub-nanosecond accuracy on commercial Wi-Fi cards. We implement these
algorithms and demonstrate a system that achieves accurate device-to-device
localization, i.e. enables a pair of Wi-Fi devices to locate each other without
any support from the infrastructure, not even the location of the access
points.Comment: 14 page
AirSync: Enabling Distributed Multiuser MIMO with Full Spatial Multiplexing
The enormous success of advanced wireless devices is pushing the demand for
higher wireless data rates. Denser spectrum reuse through the deployment of
more access points per square mile has the potential to successfully meet the
increasing demand for more bandwidth. In theory, the best approach to density
increase is via distributed multiuser MIMO, where several access points are
connected to a central server and operate as a large distributed multi-antenna
access point, ensuring that all transmitted signal power serves the purpose of
data transmission, rather than creating "interference." In practice, while
enterprise networks offer a natural setup in which distributed MIMO might be
possible, there are serious implementation difficulties, the primary one being
the need to eliminate phase and timing offsets between the jointly coordinated
access points.
In this paper we propose AirSync, a novel scheme which provides not only time
but also phase synchronization, thus enabling distributed MIMO with full
spatial multiplexing gains. AirSync locks the phase of all access points using
a common reference broadcasted over the air in conjunction with a Kalman filter
which closely tracks the phase drift. We have implemented AirSync as a digital
circuit in the FPGA of the WARP radio platform. Our experimental testbed,
comprised of two access points and two clients, shows that AirSync is able to
achieve phase synchronization within a few degrees, and allows the system to
nearly achieve the theoretical optimal multiplexing gain. We also discuss MAC
and higher layer aspects of a practical deployment. To the best of our
knowledge, AirSync offers the first ever realization of the full multiuser MIMO
gain, namely the ability to increase the number of wireless clients linearly
with the number of jointly coordinated access points, without reducing the per
client rate.Comment: Submitted to Transactions on Networkin
A Proposal for Dynamic Frequency Sharing in Wireless Networks
Wireless networks are today employed as complementary access technology, implemented on the last hop towards the Internet end-user. The shared media that wireless deployments provide and which is relevant to interconnect multiple users has a limited technical design, as only one device can be served per unit of time, design aspect that limits the potential applicability of wireless in dense environments. This paper proposes and evaluates a novel MAC-layer mechanism that extends current wireless networks with the possibility to perform downstream transmission to multiple devices within a single transmission time-frame, resulting in improved fairness for all devices. The mechanism, which is software-defined, is backward-compatible with current wireless standards and does not require any hardware changes. The solution has been validated in a realistic testbed, and the paper provides details concerning the computational aspects of our solution; a description of the implementation; and results extracted under different realistic scenarios in terms of throughput, packet loss, as well as jitter
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Concurrent Channel Access and Estimation for Scalable Multiuser MIMO Networking
This paper presents the design of MIMO/CON (“MIMO with concurrent channel access and estimation”), a PHY/MAC cross-layer design delivering throughput scalable to many users for multiuser MIMO wireless networking. By allowing concurrent launches of multiple data transmissions from multiple users, MIMO/CON can fully realize the capacity gain of a multi-antenna MIMO system. Using compressive sensing, MIMO/CON simultaneously estimates channel state information (CSI) of multiple channels from concurrently received preambles. Furthermore, MIMO/CON can boost channel utilization by allowing concurrent transmissions to exceed receive antennas momentarily. MIMO/CON has been implemented and evaluated on a lab testbed with software-defined radios. Further, simulation results suggest that MIMO/CON can achieve an improvement by up to 210% in MAC throughput over existing staggered access protocols in a 5×5 MIMO scenario.Engineering and Applied Science