Wireless 802.11 links operate in unlicensed spectrum and so must accommodate other unlicensed transmitters which generate pulsed interference. We propose a new approach for detecting the presence of pulsed interference affecting 802.11 links, and for estimating temporal statistics of this interference. This approach builds on recent work on distinguishing collision losses from noise losses in 802.11 links. When the intervals between interference pulses are i.i.d., the approach is not confined to estimating the mean and variance of these intervals but can recover the complete probability distribution. The approach is a transmitter-side technique that provides per-link information and is compatible with standard hardware. We demonstrate the effectiveness of the proposed approach using extensive experimental measurements. In addition to applications to monitoring, management and diagnostics, the fundamental information provided by our approach can potentially be used to adapt the frame durations used in a network so as to increase capacity in the presence of pulsed interference.
With regard to combined MAC PHY approaches, the present paper builds upon the packet pair approach proposed in @cite_3 @cite_23 for estimating the frame error rates due to collisions, noise and hidden terminals. See also the closely related work in @cite_35 . @cite_3 @cite_23 @cite_35 focus on time-invariant channels and do not consider estimation of temporal statistics. @cite_10 considers a similar problem to @cite_3 , but uses channel busy idle time information.
@cite_35 @cite_23 @cite_3 @cite_10
2106500630 1494686460 2147189535 2169146840
Current rate control (selection) algorithms in IEEE 802.11 are not based on accurate measurements of packet errors caused at the physical layer. Instead, algorithms act on measurements which, either implicitly or explicitly, mix physical errors with those arising from contention. In this paper we first illustrate how contention can adversely affect the performance of these algorithms, and point out the potential benefits of an ability to isolate physical packet error rate. We introduce and compare two variants of a single core idea enabling the isolation and accurate measurement of physical packet error, based on exploiting existing features of the MAC standard in a novel way. One is based on the RTS CTS mechanism, and the other on packet fragmentation. Using proof of concept experimental results from a wireless testbed, we show these mechanisms can be used to improve the performance of two existing algorithms, SampleRate and AMRR, both for individual stations and for the system as a whole, and show how incremental deployment is unproblematic. We discuss how the methodology can be integrated in a modular way into rate control algorithms with acceptable overhead. Index Terms—IEEE 802.11, rate selection, packet error rate, contention In this paper we present the first field measurements taken using a new approach proposed in [1] for measuring link impairments in 802.11 WLANs. This uses a sender-side MAC PHY cross-layer technique that can be implemented on standard hardware and is able to explicitly classify lost transmission opportunities into noise-related losses, collision induced losses, hidden-node losses and to distinguish among these different types of impairments on a per-link basis. We show that potential benefits arising from the availability of accurate and reliable data are considerable. We propose a powerful MAC PHY cross-layer approach to measuring IEEE 802.11 transmission opportunities in WLAN networks on a per-link basis. Our estimator can operate at a single station and it is able to: 1) classify losses caused by noise, collisions, and hidden nodes; and 2) distinguish between these losses and the unfairness caused by both exposed nodes and channel capture. Our estimator provides quantitative measures of the different causes of lost transmission opportunities, requiring only local measures at the 802.11 transmitter and no modification to the 802.11 protocol or in other stations. Our approach is suited to implementation on commodity hardware, and we demonstrate our prototype implementation via experimental assessments. We finally show how our estimator can help the WLAN station to improve its local performance. Current 802.11 networks do not typically achieve the maximum potential throughput despite link adaptation and cross-layer optimization techniques designed to alleviate many causes of packet loss. A primary contributing factor is the difficulty in distinguishing between various causes of packet loss, including collisions caused by high network use, co-channel interference from neighboring networks, and errors due to poor channel conditions. In this paper, we propose a novel method for estimating various collision type probabilities locally at a given node of an 802.11 network. Our approach is based on combining locally observable quantities with information observed and broadcast by the access point (AP) in order to obtain partial spatial information about the network traffic. We provide a systematic assessment and definition of the different types of collision, and show how to approximate each of them using only local and AP information. Additionally, we show how to approximate the sensitivity of these probabilities to key related configuration parameters including carrier sense threshold and packet length. We verify our methods through NS-2 simulations, and characterize estimation accuracy of each of the considered collision types.