Automatic IEEE 802.11 rate control for streaming applications

Abstract

Streaming multimedia content in real-time over a wireless link is a challenging task because of the rapid fluctuations in link conditions that can occur due to movement, interference, and so on. The popular IEEE 802.11 standard includes low-level tuning parameters like the transmission rate. Standard device drivers for today's wireless products are based on gathering statistics, and consequently, adapt rather slowly to changes in conditions. To meet the strict latency requirements of streaming applications, we designed and implemented an advanced hybrid control algorithm that uses signal-strength (SNR) information to achieve fast responses. Since SNR readings are quite noisy we do not use that information to directly control the rate setting, but rather as a safeguard limiting the range of feasible settings to choose from. We report on real-time experiments involving two laptops equipped with IEEE 802.11a wireless interface cards. The results show that using SNR information greatly enhances responsiveness in comparison to statistics-based rate controllers. Finally, we will present the results of an experiment with realtime video streaming to a moving laptop in an office-like environment. Our hybrid control algorithm effectively prevented many packets losses, thereby achieving a much higher video quality than 1 the statistics based algorithm.

A Genetic Algorithm Method for Optical Wireless Channel Control

“…Drawing parallels with the IEEE 802.11a WiFi physical layer specification, that incorporates multi-rate transmission of up to 54Mbit/s [31], and recent work on rate-adaptive transmission [32] in the IR domain, if it is found that several environments have different received powers the following method can be applied. Firstly by normalising the I scaling factors, the equality result of (8) is independent of receiver power magnitude, and secondly for different environments we can adjust for example, the pulse characteristic, in order to increase or decrease the received power to make the power distributions equal.…”

Receiver alignment dependence of a GA controlled optical wireless transmitter

“…Drawing parallels with the IEEE 802.11a WiFi physical layer specification, that incorporates multi-rate transmission of up to 54Mbit/s [25], and recent work on rateadaptive transmission [26] in the IR domain, if it is found that several environments have different received powers, the following method can be applied. Firstly, by normalising the I scaling factors, the equality result of (9) is independent of receiver power magnitude, and secondly, for different environments, we can adjust for example, the pulse characteristic, in order to increase or decrease the received power to make the power distributions equal.…”

The Snowball Effect: Detailing Performance Anomalies of 802.11 Rate Adaptation

“…Of course, there are many types of rate adaptation algorithms, but they all fundamentally rely in some way on these "trigger statistics" [3].…”

“…Delays become particularly critical in the case of real-time voice/video streaming applications, where the link conditions rapidly fluctuate due to mobility or interference. To address this problem, [3] proposes a hybrid SNR-based rate adaptation mechanism. However, this approach is limited by the very accuracy of the estimation possible in a closed-loop, low delay system -especially in the absence of standardized channel condition measurements (e.g.…”

“…[1], [2], [3]) where the authors discuss ways to differentiate between the two types of errors. Although there are several papers that propose such solutions, there are few if any papers that diagnose the cause of the problem itself.…”