Mitigating collisions through power-hopping to improve 802.11 performance

Abstract

In this article, we introduce a power-hopping technique (PH-MAC) that, by alternating between different transmission power levels, aims to deliberately cause packet capture and thereby reduce the impact of collisions in 802.11 WLANs. We first devise an analytical model of the 802.11 protocol with heterogeneous capture probabilities, and show that, depending on the network load, the capture effect can enhance the throughput performance of all nodes. We base the design of PH-MAC on the findings following from this analysis and demonstrate that important performance improvements can be achieved by exploiting the interactions between the MAC and PHY layers to mitigate collisions. Finally, to understand the feasibility of this technique in practical deployments, we present a prototype implementation of PH-MAC which relies on commodity hardware and open-source drivers. We evaluate the performance of this implementation in an indoor testbed under different network conditions in terms of link qualities, network loads and traffic types. The experimental results obtained show that our scheme can provide significant gains over the default 802.11 mechanism in terms of throughput, fairness and delay.

Acknowledgement Corruption: A New Aspect of Physical Layer Capture in IEEE 802.11 Networks

“…Note that PLC has a side effect of increasing the user throughput. In [10], a scheme is proposed to deliberately cause PLC to mitigate the impact of packet collisions (i.e., decrease of the total system throughput). From the view point of the user throughput, AC leads to "throughput decrease."…”

“…We consider two ways, which are "Moving average" and "Moving maximum." The former takes the average value in the time window, and the latter takes the maximum value near : The node executing AC avoidance algorithm ac : The set of the far nodes which can cause AC to near all : The set of the nodes in the same WiFi cell as near (1) near monitors the channel to obtain the RSSIs and transmission durations of all the nodes in all (2) for each node ∈ all do (3) If (SNR → near − SNR AP→ near ) > AC threshold then (4) ac ← ac ∪ { } (5) end if (6) end for (7) if ac ̸ = ⌀ then (8) for each node ∈ ac do (9) if (SNR near →AP − SNR →AP ) < PLC threshold then (10) ac ← ac − { } (11) end if (12) end for (13) end if (14) Minimum transmission duration ← Moving avg. or moving max.…”

“…There are existing studies that exploit PLC to enhance the network performance such as [10,17]. While AC avoidance scheme can introduce unfairness, it is beneficial to be applied to those schemes.…”

“…PLC in IEEE 802.11 has been extensively studied both analytically (e.g., [1][2][3][4]) and experimentally (e.g., [5][6][7][8][9][10]). In the existing studies, however, only the collision between data frames is considered.…”

WiFo: A diagnostic tool for IEEE 802.11 MAC

“…With ever increasing interest in WLANs, researchers have been trying to improve current protocols in terms of performance [1], [2], [3], security [4], [5], and scalability [6]. Mathematical analysis and simulations are common ways of evaluating new methods [7], [8].…”