Conference Paper

On Spatial Reuse and Capture in Ad Hoc Networks

Univ. of South Carolina, Columbia
DOI: 10.1109/WCNC.2008.291 Conference: Wireless Communications and Networking Conference, 2008. WCNC 2008. IEEE
Source: IEEE Xplore


Neighbors of both the transmitter and the receiver must keep quiet in a 802.11 wireless network as it requires bidirectional exchange, i.e., nodes reverse their roles as transmitters and receivers, for transmitting a single DATA frame. To reduce role reversals and to improve spatial reuse, a piggybacked acknowledgment based approach has been proposed to enable concurrent transmissions. Recent findings on physical layer capture show that it is possible to capture a frame of interest in the presence of concurrent interference and that the SINR threshold is dependent on the relative order in which the frame and the interference arrive at the receiver. In this paper, we show that it is possible to exploit capture and increase concurrent transmissions in wireless adhoc networks. We develop a distributed channel access scheme and demonstrate that it offers significant throughput gain particularly at lower data rates.

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    • "Thus, in packet radio, capture alone is not sufficient for successful reception, rather the receiver must be synchronized and locked onto the captured signal as well. Several research contributions analyze possible collision constellations and their effect on packet reception [14], [23], and propose a new receiver design that releases the lock when a stronger packet arrives, discards the first and receives the second packet, the so-called message-in-message (MIM) capture [14], [28]. Subsequent work applies these insights to improve network throughput. "
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    ABSTRACT: Numerous studies have shown that concurrent transmissions can help to boost wireless network performance despite the possibility of packet collisions. However, while these works provide empirical evidence that concurrent transmissions may be received reliably, existing signal capture models only partially explain the root causes of this phenomenon. We present a comprehensive mathematical model for MSK-modulated signals that makes the reasons explicit and thus provides fundamental insights on the key parameters governing the successful reception of colliding transmissions. A major contribution is the closed-form derivation of the receiver bit decision variable for an arbitrary number of colliding signals and constellations of power ratios, time offsets, and carrier phase offsets. We systematically explore the factors for successful packet delivery under concurrent transmissions across the whole parameter space of the model. We confirm the capture threshold behavior observed in previous studies but also reveal new insights relevant to the design of optimal protocols: We identify capture zones depending not only on the signal power ratio but also on time and phase offsets.
    IEEE Transactions on Wireless Communications 08/2014; 13(12):6756-6767. DOI:10.1109/TWC.2014.2349896 · 2.50 Impact Factor
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    ABSTRACT: Recent experimental studies on physical layer capture in 802.11 based networks have demonstrated that the minimum signal-to-interference ratio required for successful reception of a frame depends upon the order of arrivals of the sender's frame and the interference, and it is much less when the sender's frame arrives earlier. This differential capture capability (DCC) leads to a very small interference range around the receiver once it starts receiving a frame, and hence it allows considerable reduction in the required carrier sensing range. While the DCC feature of receivers helps alleviate some hidden and exposed terminal problems, there still remains many exposed nodes. In this paper, we further exploit the DCC feature to mitigate the problem of these exposed terminals that remain even after optimum reduction in carrier sensing range. We propose a liberal carrier sensing scheme that helps identify some of the exposed prospective receivers by using some already available local information and allow them to initiate secondary sessions. Through extensive simulations we demonstrate that the proposed scheme offers significant throughput gain over the conventional carrier sensing scheme that ignores the DCC feature.
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    ABSTRACT: Recent experimental results have shown that the minimum signal-to-interference ratio required at a receiver (CP<sub>th</sub>) depends on the order of arrival of the overlapping frames. For a given sender-receiver distance, this differential capture capability of a receiver leads to two distinct interference ranges (r<sub>i</sub>) around the receiver, and its value is much smaller when the sender's frame arrives earlier. This feature also suggests a possibility of increased spatial reuse by allowing the (secondary) nodes outside the primary receiver's r<sub>i</sub> to communicate concurrently once the primary receiver starts its DATA reception. In this paper, we propose a liberal carrier sensing (LCS) scheme wherein some already available information at an otherwise 'exposed' receiver are exploited to help decide when it is safe to respond to a secondary transmission request. The proposed modification in the carrier sensing approach results in a significantly improved spatial reuse, thereby increasing overall system throughput. Our simulation studies show that, compared to the conventional carrier sensing scheme with differential capture capable receivers, the end-to-end TCP throughput with LCS can be improved by more than 20% in regular topologies and up to about 9% in random topologies.
    Communications (ICC), 2010 IEEE International Conference on; 06/2010
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