Side Channel: Bits over Interference
ABSTRACT 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.
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ABSTRACT: The IEEE 802.11 wireless LAN (WLAN) is based on carrier sense multiple access with collision avoidance (CSMA/CA) protocol. CSMA/CA uses a backoff mechanism to avoid collisions among stations (STAs). One disadvantage of backoff mechanisms is that STAs must wait for some period of time before transmission, which degrades spectral efficiency. Moreover, a backoff algorithm cannot completely avoid collisions. We have proposed a novel medium access control (MAC) scheme called the visual recognition-based medium access control (VRMAC) scheme, which uses an LED-camera communication technique. STAs send media-access request messages by blinking their LEDs in VRMAC scheme. An access point (AP) receives the messages via its camera, and then allocates transmission opportunities to the STAs by transmitting control frames. Since the transmission rate of the LED-camera communication is lower than WLAN transmission, the delay of access requesting causes and it could decrease the system throughput of the VRMAC system based WLAN. We reveal the effect of the delay for TCP flows and propose enhanced access procedures to eliminate the effect of the delay. Our simulation results demonstrate that VRMAC scheme increases the system throughput in UDP and TCP traffic. Moreover, the scenario-based evaluations reveal that VRMAC scheme also decreases the session delay which is a metric of quality of experience (QoE) for TCP applications. key words: WLAN, visual MIMO, medium access control, CSMA/CA, quality of experience, optical camera communicationsIEICE Transactions on Communications 01/2015; E98-B(5):917-926. DOI:10.1587/transcom.E98.B.917 · 0.33 Impact Factor
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ABSTRACT: Many media exist for communication, such as LTE, IEEE 802.11 wireless local area networks (WLANs), millimeter-wave communications, and visible light communications (VLCs), and a lot of research has been conducted to find methods to improve the performance of each medium. However, the use of a single medium for communication limits the performance upper bound that can be achieved by using more than one medium for communication. Moreover, some media are widely used, while others are not because their use cases are limited. Therefore, the more commonly used media still suffer from a lack of bandwidth, while bandwidth for other media types is abundant. In this paper, we propose a heterogeneous media communications (HeMCOM) framework, where multiple media are used for leveraging the abundant bandwidth and increasing the total communication performance. HeMCOM focuses on leveraging the difference of the PHY and MAC characteristics of each medium. This paper summarizes the HeMCOM concept, introduces related works from the point of view of this concept, and discusses the possibility of using several types of media.IEEE ICCE 2015, Las Vegas, Nevada, US; 01/2015
Article: Managing Contention with Medley[Show abstract] [Hide abstract]
ABSTRACT: As WLANs achieve gigabit per second speeds, they will need to support users with a wide range of workloads, ranging from VoIP and Web clients to data backup, file transfers, and streaming high-definition video. Unfortunately, channel efficiency degrades severely in these scenarios under existing MAC protocols due to contention and back-off overheads. Moreover, small yet latency-sensitive flows suffer disproportionally as load increases. We present Medley, a system that leverages frequency-based contention to allocate subchannels in an OFDMA-based link layer in a delay-fair manner. In contrast to traditional CSMA schemes in which each node competes uniformly for the channel, Medley ensures that nodes with smaller service rates are served before those with heavier demand; the more bandwidth a node consumes, the larger its packet average delay will become. An initial implementation of Medley on a software defined radio platform demonstrates its feasibility in a small network, while more comprehensive simulation results show its benefits under a wider range of conditions. Medley delivers delay fairness while remaining over 94 percent efficient in the face of massive over-subscription.IEEE Transactions on Mobile Computing 03/2015; 14(3):579-591. DOI:10.1109/TMC.2014.2315822 · 2.91 Impact Factor