Spectrum Utilization and Congestion of IEEE 802.11 Networks in the 2.4 GHz ISM Band

Wi-Fi technology, plays a major role in society thanks to its widespread availability, ease of use and low cost. To assure its long term viability in terms of capacity and ability to share the spectrum efficiently, it is of paramount to study the spectrum utilization and congestion mechanisms in live environments. In this paper the service level in the 2.4 GHz ISM band is investigated with focus on todays IEEE 802.11 WLAN systems with support for the 802.11e extension. Here service level means the overall Quality of Service (QoS), i.e. can all devices fulfill their communication needs? A crosslayer approach is used, since the service level can be measured at several levels of the protocol stack. The focus is on monitoring at both the Physical (PHY) and the Medium Access Control (MAC) link layer simultaneously by performing respectively power measurements with a spectrum analyzer to assess spectrum utilization and packet sniffing to measure the congestion. Compared to traditional QoS analysis in 802.11 networks, packet sniffing allows to study the occurring congestion mechanisms more thoroughly. The monitoring is applied for the following two cases. First the influence of interference between WLAN networks sharing the same radio channel is investigated in a controlled environment. It turns out that retry rate, Clear-ToSend (CTS), Request-To-Send (RTS) and (Block) Acknowledgment (ACK) frames can be used to identify congestion, whereas the spectrum analyzer is employed to identify the source of interference. Secondly, live measurements are performed at three locations to identify this type of interference in real-live situations. Results show inefficient use of the wireless medium in certain scenarios, due to a large portion of management and control frames compared to data content frames (i.e. only 21% of the frames is identified as data frames)

Effects of Data Frame Size Distribution on Wireless Lans

The continuous need to replace cables and deploy mobile devices in the communications industry has led to very active research on the utilization of wireless networks. IEEE 802.11 WLAN is known to achieve relatively small throughput performance compared to the underlying physical layer’s transmission rate and this is as a result of large overhead information composed of medium access control header, physical layer preamble information back-off duration control frames (ACK) transmissions and even inter-frame spaces. This paper provides an overview of frame size distribution using the dual fixed frame size as a case in point and subsequently a performance evaluation in a multi-user transmission channel condition is carried out. The distribution of frame size and its effect on the throughput is also investigated. This is done through comparison of various scenarios such as fixed frame size distribution and dual-fixed frame size distribution. The dual- fixed frame size distribution case has both equality and inequality cases and both are investigated. The case of equal frames was found to have improved marginal throughput compared to the other cases. The analysis and measurement results from OPNET simulation has shown that an equal fixed frame size distribution can be efficient in optimizing useful data