Side Channel: Bits over Interference
DOI: 10.1109/TMC.2011.158 Conference: Proceedings of the 16th Annual International Conference on Mobile Computing and Networking, MOBICOM 2010, Chicago, Illinois, USA, September 20-24, 2010
Interference is a critical issue in wireless communications. In a typical multiple-user environment, different users may severely interfere with each other. Coordination among users therefore is an indispensable part for interference management in wireless networks. It is known that coordination among multiple nodes is a costly operation taking a significant amount of valuable communication resource. In this paper, we have an interesting observation that by generating intended patterns, some simultaneous transmissions, i.e., "interference,” can be successfully decoded without degrading the effective throughput in original transmission. As such, an extra and "free” coordination channel can be built. Based on this idea, we propose a DC-MAC to leverage this "free” channel for efficient medium access in a multiple-user wireless network. We theoretically analyze the capacity of this channel under different environments with various modulation schemes. USRP2-based implementation experiments show that compared with the widely adopted CSMA, DC-MAC can improve the channel utilization efficiency by up to 250 percent.
Available from: Yong Lu
- "It is a hot topic recently to provide a separate control plane on the same channel concurrently with data transmissions. In , a free coordination channel is built by generating intended interference patterns. In , Flashback carries the control messages by sending short high-powered flashes. "
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ABSTRACT: Coordination among users is an indispensable part
in wireless networks for efficient medium access. Alone with
the rapid increase of transmission rate, however, coordination
time becomes insufferable. We present AFD, namely asymmetric
full duplex, to achieve high coordination efficiency at nearly
zero overhead. In AFD, channel contention is performed simultaneously
with data transmission. We propose a 3D pipeline
contention scheme where the contention process is divided into
several parallel stages and executed in a pipelined manner in
a 3D domain specified by time, frequency and spatial antenna.
To mitigate the interference between the data packet and the
contention signal, we adopt a singleton PN sequence as a
contention pilot. AFD provides a novel network-scale full duplex
capability. The performance is evaluated by both simulations
and measurements in a testbed. AFD outperforms IEEE 802.11
significantly, i.e., the Jain’s fairness index is around 0.95 with a
throughput gain up to 120%.
Available from: Jiang Xiao
- "They reduce the MAC layer overhead by representing control information in frequency domain. Another type of work, like Side channel , uses "interference pattern" to reduce the control overhead without interference cancellation. And our previous work, hjam  and FAST  utilize interference cancellation to transmit both control information and data packets together. "
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ABSTRACT: It is known that current fixed spectrum assignment policy has made the spectrum resource significantly underutilized. As a promising solution, cognitive radio emerges and shows its advantages. It allows the unlicensed users to opportunistically access the spectrum not used by the licensed users. To ensure that the unlicensed users can identify the vacate spectrum fast and accurately without interfering the licensed users, cooperative sensing is explored to improve the sensing performance by leveraging spatial diversity. However, cooperation gain can be compromised dramatically with cooperation overhead. Furthermore, when sensing decisions are made, contention on spectrum access also contributes a lot to the control overhead, especially in the distributed networks. Motivated by this, we propose a novel MAC design, termed Frequency domain Cooperative sensing and Multi-channel contention (FCM) for Cognitive Radio Ad Hoc Networks (CRAHNs). FCM is proposed for OFDM (Orthogonal Frequency Division Multiplexing) modulation based communication systems, which moves cooperative sensing and multi-channel contention from time domain into frequency domain. Therefore, control overhead caused by cooperation and contention can be significantly reduced. Meanwhile, the sensing and access performance can be both guaranteed. Extensive simulation results show that FCM can effectively reduce the control overhead, and improve the average throughput by 220% over Traditional Cooperative MAC for CRAHNs.
Available from: arxiv.org
- "Carrier sense, dual busy tones and collision notifications are binary signaling mechanisms, not suited for transmitting numeric information, as required by message passing protocols. Another recent physical layer extension  aims at realizing a side-channel over spread-spectrum based protocols through perturbations of certain chips comprising a transmitted symbol. These perturbations are in turn compensated for by the normal error correcting codes employed in data transmission, thus allowing in most cases for the payload to be decoded correctly , and they are also detected by a special pattern analyzer, allowing fo rthe transmission of side information. "
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ABSTRACT: In wireless networks, the presence of interference among wireless links in-
troduces dependencies among flows that do not share a single link or node. As a
result, when designing a resource allocation scheme, be it a medium access
scheduler or a flow rate controller, one needs to consider the interdependence
among nodes within interference range of each other. Specifically, control
plane information needs to reach nearby nodes which often lie outside the
communi- cation range, but within the interference range of a node of interest.
But how can one communicate control plane information well beyond the existing
communication range? To address this fundamental need we introduce tag
spotting. Tag spotting refers to a communication system which allows re- liable
control data transmission at SNR values as low as 0 dB. It does this by
employing a number of signal encoding techniques including adding redundancy to
multitone modulation, shaping the spectrum to reduce inter-carrier interfer-
ence, and the use of algebraic coding. Making use of a detection theory-based
model we analyze the performance achievable by our modulation as well as the
trade-off between the rate of the information transmitted and the likelihood of
error. Using real-world experiments on an OFDM system built with software
radios, we show that we can transmit data at the target SNR value of 0 dB with
a 6% overhead; that is, 6% of our packet is used for our low-SNR decodable tags
(which carry up to a couple of bytes of data in our testbed), while the remain-
ing 94% is used for traditional header and payload data. We also demonstrate
via simulations how tag spotting can be used in implementing fair and efficient
rate control and scheduling schemes.
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