Saleem Bhatti, Computer Science, University of St Andrews, UK.  

IEEE 802.11 / WiFi

The IEEE 802.11 / WiFi communication protocols for wireless local area network (WLAN) access has evolved over a number of years. With every new version of the standard, the intention is to improve performance, mainly in terms of the possible data transfer speed. As well as considering speed of data transfer, the work here has considered energy usage, as well as impact on applications, and deployment / operational issues.

M. Abu-Tair, S. N. Bhatti. IEEE 802.11ac MU-MIMO Wireless LAN cells with Legacy Clients. AINA 2017 - 31st IEEE Intl. Conf. Advanced Information Networking and Applications. Taipei, Taiwan. Mar 2017.
| PDF | .bib | 10.1109/AINA.2017.46 |   abstract We provide an empirical evaluation of an IEEE 802.11ac Wireless Local Area Network (WLAN) cell with Multiple User Multiple Input Multiple Output (MU-MIMO) technology. We conducted our experiments on a testbed comprising consumer equipment under different office scenarios using 40MHz and 80MHz channels. This is the first performance study of MU-MIMO with 802.11ac in an operational scenario using a commercial access point. We find that, for clients that do not support MU-MIMO, operating in a cell that has MU-MIMO enabled may result in reduced performance.
M. Abu-Tair, S. N. Bhatti. Impact of cell load on 5GHz IEEE 802.11 WLAN. PAEWN 2017 - 12th Intl. Wkshp. Performance Analysis and Enhancement of Wireless Networks. Taipei, Taiwan. Mar 2017.
| PDF | .bib | 10.1109/WAINA.2017.27 |   abstract We have conducted an empirical study of the latest 5GHz IEEE 802.11 wireless LAN (WLAN) variants of 802.11n (5GHz) and 802.11ac (Wave 1), under different cell load conditions. We have considered typical configurations of both protocols on a Linux testbed. Under light load, there is no clear difference between 802.11n and 802.11ac in terms of performance and energy consumption. However, in some cases of high cell load, we have found that there may be a small advantage with 802.11ac. Overall, we conclude that there may be little benefit in upgrading from 802.11n (5GHz) to 802.11ac in its current offering, as the benefits may be too small.
M. Abu-Tair, S. N. Bhatti. Introducing IEEE 802.11ac into existing WLAN deployment scenarios. WiOpt 2015 - 13th Intl. Symp. Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiNMeE 2015 - IEEE Intl. Workshop on Wireless Networks: Measurements and Experimentation). Mumbai, India. May 2015.
| PDF | .bib | 10.1109/WIOPT.2015.7151029 |   abstract In mature wireless LAN (WLAN) deployments, we show that introducing 802.11ac could have little benefit compared to existing 802.11n deployments. Using a testbed with common characteristics for an existing WLAN deployment (such as an office environment), we compare throughput for 802.11ac and 802.11n (in both 5GHz and 2.4GHz bands). We find that 802.11ac has lower throughput than for 802.11n for our testbed configuration. We also provide an evaluation of energy usage for 802.11ac and 802.11n.
M. Abu-Tair, S. N. Bhatti. Upgrading 802.11 deployments: a critical examination of performance. AINA 2015 - IEEE 29th Intl. Conf. Advanced Information Networking and Applications. Seoul, Korea. Mar 2015.
| PDF | .bib | 10.1109/AINA.2015.278 |   abstract The increased demand for communications and Internet access makes Wireless Local Area Networks (WLANs) one of the most popular solutions for network connectivity. In this paper, we examine the performance and the energy efficiency of WLANs in 2.4 GHz and 5 GHz and discuss paths for upgrading. Our results show that it is worth upgrading to the 5 GHz bands from the 2.4 GHz band for 802.11n, especially for applications that are sensitive to packet loss. We also show that it is little benefit in upgrading from 802.11n 5 GHz to its successor 802.11ac in terms of performance and energy efficiency. We consider overall performance as well as the energy efficiency of 802.11n 2.4 GHz, 802.11n 5 GHz and 802.11ac protocols, all with 40MHz channels, to give a typical 802.11 office scenario. It is clear that 802.11ac can achieve slightly higher throughput compared to 802.11 for flows of large packets. However, the comparatively small benefits of 802.11ac may not justify the cost of buying and deploying new equipment for the upgrade.
M. Abu-Tair, S. N. Bhatti. Energy Usage of UDP and DCCP over 802.11n. AINA 2014 - IEEE 28th Intl. Conf. Advanced Information Networking and Applications. Victoria, Canada. May 2014.
| PDF | .bib | 10.1109/AINA.2014.40 |   abstract We show that the Datagram Congestion Control Protocol (DCCP) provides ~10% -- ~40% greater energy efficiency than the User Datagram Protocol (UDP) in a wireless LAN (WLAN) client. Our empirical evaluation uses a testbed comprised of consumer components and opensource software to measure typical performance that can be expected by a user, rather than highly-tuned performance which most users will not be able to configure. We focus our measurements on a scenario using IEEE 802.11n at 5GHz as energy efficiency will be particularly important to mobile and wireless users. We consider overall performance as well as the energy efficiency of the protocol usage to give a rounded comparison of UDP and DCCP. Overall, we see there would be great benefit in many applications using DCCP instead of UDP.
M. Tauber, S. N. Bhatti, N. Melnikov, J. Schoenwaelder. The Case for Heterogeneous WLAN Environments for Converged Networks. ICNC 2013 - IEEE Intl. Conf. Computing, Networking and Communications. San Diego, CA, USA. Jan 2013.
| PDF | .bib | 10.1109/ICCNC.2013.6504056 |   abstract We demonstrate that in a future converged network scenario, it may be beneficial to allow selection of 802.11 variant based on application requirements. We analyse traces from the campus network from the University of Twente, comprising ∼5000 users. We have evaluated a performance envelope derived from testbed experiments for individual IEEE 802.11 variants and compare these with the traffic patterns from the campus network. From our comparison, we find that specific IEEE 802.11 variants (e.g. 802.11g or 802.11n) may be better suited to specific applications, such as video streaming, rather than using a single WLAN standard for all traffic.
M. Tauber, S. N. Bhatti. Low RSSI in WLANs: Impact on Application-Level Performance. ICNC 2013 - IEEE Intl. Conf. Computing, Networking and Communications. San Diego, CA, USA. Jan 2013.
| PDF | .bib | 10.1109/ICCNC.2013.6504066 |   abstract Widespread use of wireless LAN (WLAN) may soon cause an over-crowding problem in use of the ISM spectrum. One way in which this manifests itself is the low Received Signal Strength Indication (RSSI) at the WLAN stations, impacting performance. Meanwhile, the IEEE 802.11 standard is being evolved and extended, for example with new coding schemes and the 802.11n standard, which makes use of 5GHz and 2.4GHz. We report on measurements of the upper and lower bounds of performance with good and poor RSSI in 802.11g and 802.11n. We find that in operation under poor (low) RSSI, performance is indeed impacted. In some cases the impact is such that there may be little benefit in using the newer 802.11n over the mature 802.11g.
M. Tauber, S. N. Bhatti. The Effect of the 802.11 Power Save Mechanism (PSM) on Energy Efficiency and Performance During System Activity. GreenCom 2012 - IEEE Intl. Conf. Green Computing and Communications. Besancon, France. Nov 2012.
| PDF | .bib | 10.1109/GreenCom.2012.81 |   abstract 802.11 WLAN is a popular choice for wireless access on a range of ICT devices. A growing concern is the increased energy usage of ICT, for reasons of cost and environmental protection. The Power Save Mode (PSM) in 802.11 deactivates the wireless network interface during periods of inactivity. However, applications increasingly use push models, and so devices may be active much of the time. We have investigated the effectiveness of PSM, and considered its impact on performance when a device is active. Rather than concentrate on the NIC, we have taken a system-wide approach, to gauge the impact of the PSM from an application perspective. We experimentally evaluated performance at the packet level and system-wide power usage under various offered loads, controlled by packet size and data rate, on our 802.11n testbed. We have measured the system- wide power consumption corresponding to the individual traffic profiles and have derived application-specific effective energy-usage. We have found that in our scenarios, no significant benefit can be gained from using PSM.
M. Tauber, S. N. Bhatti, Y. Yu. Towards Energy-Awareness In Managing Wireless LAN Applications. NOMS 2012 - IEEE Network Operations and Management Symp.. Maui, Hawaii, USA. Apr 2012.
| PDF | .bib | 10.1109/NOMS.2012.6211930 |   abstract We have investigated the scope for enabling WLAN applications to manage the trade-off between performance and energy usage. We have conducted measurements of energy usage and performance in our 802.11n WLAN testbed, which operates in the 5 GHz ISM band. We have defined an effective energy usage envelope with respect to application-level packet transmission, and we demonstrate how performance as well as the effective energy usage envelope is effected by various configurations of IEEE 802.11n, including transmission power levels and channel width. Our findings show that the packet size and packet rate of the application flow have the greatest impact on application- level energy usage, compared to transmission power and channel width. As well as testing across a range of packet sizes and packet rates, we emulate a Skype flow, a YouTube flow and file transfers (HTTP over Internet and local server) to place our results in context. Based on our measurements we discuss approaches and potential improvements of management in effective energy usage for the tested applications.
M. Tauber, S. N. Bhatti, Y. Yu. Application Level Energy and Performance Measurements in a Wireless LAN. GreenCom 2011 - IEEE/ACM Intl. Conf. Green Computing and Communications. Chengdu, Sichuan. Aug 2011.
| PDF | .bib | 10.1109/GreenCom.2011.26 |   abstract We present an experimental evaluation of energy usage and performance in a wireless LAN cell based on a test bed using the 5 GHz ISM band for 802.11a and 802.11n. We have taken an application-level approach, by varying the packet size and transmission rate at the protocol level and evaluating energy usage across a range of application transmission rates using both large and small packet sizes. We have observed that both the application's transmission rate and the packet size have an impact on energy efficiency for transmission in our test bed. We also included in our experiments evaluation of the energy efficiency of emulations of YouTube and Skype flows, and a comparison with Ethernet transmissions.